Why You Need Domain Knowledge

This is the Feinwerkbau P11 Piccolo Air Pistol. It costs somewhere around $1,500 and looks like it is mainly designed for people doing competition. The black barrel is what shoots the pellet and the silver barrel is the compressed air.

If you have a gun that runs on compressed air, it would be nice to know how much air you have left wouldn’t it? I’m not sure the design was fully thought through.

I don’t know the story of the gun, but I do know that you shouldn’t need to point the barrel toward your face to read a gauge.

When I see something like this I like to stop and think about whether or not I make the same mistakes in my field of software development. Poor design decisions aren’t limited to guns.

Domain Experts & Software

Mistakes in software design aren’t always as easy to spot, but often it comes down to the same thing. To design something you must have at least a basic level of domain knowledge.  That doesn’t means you have to be a world famous chef in order to write a recipe webapp, but you need to make sure you at least know the basics.

If you don’t have the domain knowledge, then partner with someone who has it. I’ve been working on an application for the past year where I partnered with non-technical people who know the industry. It would have been easy to discount the value of people who can’t really contribute to writing the software, but it has been well worth it. Not only do they have the knowledge of the industry that let us create the right product, but they know the people who would be interested in buying it.

Just having a good idea and the ability to create software isn’t enough to succeed. You can significantly increase your chances by partnering with people who are in your target market who can use the product from the very beginning. If you choose carefully you can get not only their expertise in the domain, but also their network of connections–people who have the exact same problems that your product can fix.

Now some people have pointed out that a company that makes guns probably has much more domain knowledge about air powered pistols than I do. That is probably true. I  have a reasonable amount of domain knowledge about guns including some classes, etc. One of the first things you learn anytime you learn anything about guns is not to point it at your face.

But this brings up an important point. Having domain knowledge and applying it are two different things.

Testing Software

When it comes to software, we have the luxury of testing. Get your code to a usable state and then let someone use it. Sometimes you’ll find that there is a disconnect between what works and what the domain experts tell you will work. This doesn’t mean you have a bad expert. They may be an expert in their field, but that doesn’t mean they are an expert at explaining it to you. Often this means that as part of the development process they will say you need to do X and then after they use it, change their mind and say you need to do Y.

This isn’t a bad thing and is a natural part of building something correctly. What you can do  is try to make sure that those experiences come early and with as little pain as possible.

I was working on a project awhile back where we put most of our effort into the public facing portion of a web app. The backend was a mess through. It worked but it was very ugly. But it let us launch quickly and get some real world experience. By the time we were ready to redo the backend, the people who were using it had a lot better idea of what they needed. Many of the initial things that they wanted to change turned out to be irrelevant, but there were a bunch of other assumptions that it turned out were wrong and needed to be changed.

Domain expertise will usually get you headed in the right direction, but you don’t know if you’ve done the right thing until someone is actually using your code.


70 Replies to “Why You Need Domain Knowledge”

  1. “Customers who purchased this product also purchased: First Aid Only 6″ X 9″ Instant Cold Compress, 3M Medipore H Soft Cloth Surgical Tape, Nexcare Opticlude(TM) Orthoptic Eyepatch”

  2. Nice piece. You mention partnering with people who “know the industry”… what kinds of benefits did this bring you? Did they have good connections, were they better able to get you funding? Also, were you working on their ideas or did you come up with something together…

    Lastly, where did you go to find trustworthy, hardworking non-technical cofounders? I’m asking because I’m in a similar pickle…

    1. They were people I had worked with as a consultant previously. The benefit was they could say, “Yes that sounds like a good feature, but we’d never use that in our work.” They also took care of finding the first clients we sold the system to–just by asking people in their network that they were already working with.

      The product is a ticket/registration system aiming at people/companies who need something a bit more customizable than EventBrite, etc. but don’t have the resources or expertise to build it themselves. The people I worked with offer booking services for speakers and entertainers that fall into this segment.

      As individuals, we split the development cost. My company billed our partnership just like any other client and I paid half and they paid half. That helped keep things fair on the development side of things and kept us from needing to go out and get funding.

      Does that help answer your questions?

  3. Pity that there’s nowhere else to put that gauge – if you put it on the sides, it unbalances the weapon and/or makes the canister weaker/makes it impossible to remove by screwing… :) There’s sometimes compromises to every solution!

  4. Just a note about the gun (from a person shooting air rifles for a long time): I don’t really think there is another way to put the gauge. One side of the cylinder is obviously connected to the gun, and putting it on the sides wouldn’t work because it would make the cylinder not round. The cylinder of an air rifle/gun is removed by rotating it when it’s refilled or stored. If there is something sticking out of the side it wouldn’t be able to rotate because it would hit the barrel, and be clunky when storing many cylinders in one place.

    Anyway, when reading the gauge (and all other times you aren’t shooting), you should always keep the gun unloaded and the loading bay open, this makes it impossible to shoot the gun because the air would escape at the loading bay.

    1. This can actually be solved very easily. The cover plate on the gauge can be modified to allow the needle to extend to the edge, or even slightly past it. That would make it visible from a rear angle. You would then mark the status on the outside of the canister rather on the gauge itself.

      1. Or angle the gauge so you view it from below. Heck you could probably make the gauge face straight down, using a smaller diameter gauge so it doesn’t stick out.

        I have to also add that the comments that there isn’t really anywhere else to put it represent the exact domain knowledge that Mark is talking about. So even the counter-example proves his main point. :)

    2. Then you’d either:

      1) Go digital, and put the display on top (aka DSLR cameras).

      2) Use a barrel (cylindrical) shaped gauge – then you’d use the depth of the cylinder to show the charge as opposed to the standard clock-style. That’s balanced, and must be read from the side so it’s safer..

      3) Make the gauge pivotable. Problem solved, especially if pivotted upwards and combined it with an automatic safety.

  5. Couldn’t agree more. Especially about the ‘getting-it-to-a-useable-state-and-trying-it-out’ part.

    For my project I counted myself as a partial a domain-expert but then I would defer to the real domain expert when I wasn’t sure. Even then there were a lot of things that I thought that we needed that we really didn’t. I ended up building the thing that they needed not what I thought they needed.

    Turns out there’s a big difference …

  6. Hi Mark,
    Just to answer your question about the pistol, it’s an interesting counterpoint that highlights that you need domain knowledge to ask a question too.

    You see, that’s an ISSF pistol. It’s stored disassembled to save wear and tear on the regulator. You check the manometer when you take the cylinder out of the case to screw it into the pistol, and you check it when filling the cylinder off a dive bottle. In neither case is the cylinder attached to a pistol at the time, so you never wind up looking down the barrel of the pistol.

    And since that’s the first rule anyone who ever picks up a firearm in target shooting is taught, and since it’s in every rulebook in every shooting sport, and since ISSF has a better safety record than, well, just about every sport out there (in Ireland, we’ve been doing this since 1840-odd with no injuries in formal target shooting), it’s not really as big a problem as it seems.

    Also, the manometer is designed so you can read it from up to 80 degrees off-axis, not so you don’t look down the barrel, but so that if a thread strips when filling the cylinder, you’re not on-axis when it tears across the room at mach one. See, everyone thinks the pistol is the dangerous bit, but even if you shot yourself in the head with it at point blank range, it’s unlikely to penetrate the skull (it has, regrettably, been tried in the UK by a man trying to commit suicide). The really dangerous bit is the cylinder itself, which has about as much stored energy when fully charged as a hand grenade. Hence the manometer – which isn’t calibrated in number of shots fired, but in zones (from Empty and safe for airline travel to Match with enough air for 40-60 shots, to Overpressure which is known colloquially as Oh Shit Run territory).

    And yes, we know about that danger and take appropriate steps there too.

    User Interfaces. Always trumped by training and contextual knowledge.

    1. You’re so right about context and stuff, but if anything this makes it a better example. It’s an obvious danger, and the solution is a matter of good training. Take that to software, and I would say that you’re in the territory of documentation and help-files.

      I got taught very basic weapon safety by an ex-Army sergeant. That photograph gave me a cold chill. He also told me that there were drills for a weapon inspection, which you didn’t need to use for my father’s shotgun, but which you would use to inspect the barrel of a Lee-Enfield.

      I’ve learned since of other apparently crazy exceptions to the basic rule. Again, safe when done according to the documented drills.

      Some software writers couldn’t document a barn door from the inside.

    2. Thanks for the information about the gun. You explanation makes sense as to why the gauge can’t be built into the the gun instead of the canister.

      Obviously this isn’t something you buy at Wal-mart to go plink around in your back yard, so the people using it should be basically professionals at handling this type of gun. Still I’d argue that putting any type of information readout on the end like that is about like putting a self destruct button right next to the radio power button in your car.

      As far as design, it seems some type of linear scale on the side of the canister would be a bit more safe–even for people that know not to look in the barrel of the gun.

      1. I can see why you’d think that the design was bad, but that’s the thing about domain knowledge – without it, that’s a bad design. With it, you realise that shooters don’t care about their air pressure during a match and so never have a motive to check it when the cylinder is in the pistol.

        (There’s an air regulator in the pistol. When the manometer’s in the green, which is is for far more shots than there are in a match, the pressure behind the pellet is constant. When the pressure drops, you get an indication from the point of impact and the sound of the shot, you don’t need to look at the manometer, and even if you did, you can look at it from up to 80-odd degrees off-axis anyway. So it’s just not an issue).

        And while an untrained newbie out in the boonies who’s never seen a range *might* not have the training that normal users of the pistol have, it’s a $1500 pistol. It’s not something people buy on a whim without training.

        The idea of a linear scale is interesting, but there’s a larger problem – it’d show you the pressure in the tank during normal use (ie. during a match). And that would be a design flaw, because in the sport these are used for, the mental game is everything (target shooting is not about speed or strength, it’s about control and the mental game there is critical). You start throwing superflous information into a shooter’s visual field like that and you will adversely affect their performance (and when you spend $1500 on your sports equipment, you like it to benefit your performance, not the other way round!). Again, domain knowledge is key here.

        There is the practical problem, of course (and this is a nice counterpoint too) – with a linear scale on the side, you’d have to have a weight on the other side inside the cylinder because even weight distribution is critical. That reduces interior volume and the shape change inside the cylinder would introduce stress points in the design, so you’d have to beef up the material there or risk a catastrophic failure of a 200 bar pressure vessel a few inches from your fingers. So now you have a heavier cylinder, which adversely affects your mental game, and doesn’t have as much compressed air in it, and is probably more expensive to make. I don’t think that’s a better design, and worse yet, it’s not as safe because now you *will* encourage people to turn the pistol through 90 degrees to read the gauge… and thus point it directly at the shooter beside them on the firing line who may not even see the danger they’ve now been exposed to.

        The existing design is the current end product of decades of research, development and trials – it’s the way it is for a lot of good reasons…

        1. Your argument has been that the people using this gun are so disciplined they won’t try to to look at the gauge and because it doesn’t present any useful information for them during the match. Based on that, you feel the design is good and doesn’t present any safety hazard for the intended audience.

          However, if the information was on the side, you feel these same people (who are so disciplined that they would never look at the information when it is on the end of the gun) would get distracted by the information being presented on the side and it would make them miss the bullseye.

          This seems contradictory to me. If someone is likely to get distracted by information, I think it is better for the result of a distraction to getting a worse score than pointing the barrel toward their optic nerves.

          When it comes to guns on a shooting range, think of an invisible plane that is perpendicular to the line of fire. When the gun is pointed in a safe direction (directly at the target) the line of fire is 90 degrees from the plane in every direction. I feel that the design should be optimized to minimize the reduction in the angle between the safe line of fire (pointed toward the target) and the plane. Information that is displayed toward the target is less safe than information that is displayed at a 90 degree angle to the line of fire.

          I understand the weight and balance considerations, but I’m pretty sure that is just a design issue–you just build it so it is balanced. As far as expense, you may have a point, I believe I’ve seen things like this done in a way that wouldn’t be any more expensive than the gauge, but this type of design isn’t my field. But I’m pretty sure there is a design that would meet all of the necessary criteria–including cost and safety. However, I understand if you disagree.

          Thanks for taking the time to comment!

        2. It’s not so much that people are so disciplined that they won’t look so much as it is that the information on the gauge is of no use whatsoever when shooting that there’s no motivation to look at all, combined with training in how to properly use the pistol in the first place.

          Having the information in the visual field *is* a distraction when shooting therefore because it is completely superfluous but provides a point for the eye to jump to. In our sport, that’s a design flaw in the user interface.

          The weight and balance issues are not minor, as you imply; they are critical to the function of the pistol and are a sufficiently critical factor as to cause people to make both purchasing and design decisions. These are highly specific tools for a highly specific task; if you seriously compromise the primary function of the pistol in order to satisfy a designers issue with a user interface, especially one which for users isn’t even an issue in the first place, then your design fails.

          The expense, is possibly a secondary concern; but the problem with the interior shape and stress points in the cylinder if you introduced a linear scale and corresponding weights is not; it’s a fundamental engineering and safety concern. Which is mildly ironic, considering.

          The end point I’m trying to make is that the example you’ve chosen as an example of bad design because of poor domain knowledge, is actually an example of a highly evolved design which is the best possible design when you have that domain knowledge, and which isn’t a bad design when used in that domain because of the domain knowledge and training possessed by the practitioners.

          That’s a critical design lesson in and of itself.

        3. What I take issue with is that this is the “best possible design,” although I understand your reasoning as to why it is. But I do appreciate you taking the time to explain various aspects of the sport and gun design. I also enjoyed looking through your website–particularly the electronic displays of where the shots hit.

    3. Thank you for this post. I was about to post something very similar. Ironic that the author made the same mistake in using this example as he is warning against…

      1. It’s rather ironic that the author warns against looks over substance, when he himself did not research on his example properly, and judges the product solely on its shiny looks and how he, a novice – the unintended user, would use it.

        Doubtful credibility of the author here. He owes the designer of the product a big apology for all the bad reviews it gained as a result on Amazon.

        1. Maddy – I appreciate that you took the time to leave a comment. I recognize that some people feel that this design represents the best possible way to indicate the pressure in the cylinder. If this is your stance, I respectfully disagree as I feel there are other designs that would not place information facing the non-safe side of the gun.

  7. A colleague (who shoots as a hobby) says that the design is pretty much standard for sporting air pistols and rifles. So I wonder: How has a whole community come to accept bad designs? Or is there some non-obvious reason that makes this not a bad design, even though to non-domain experts it seems crazy?

  8. I run a small boutique marketing agency and this is EXACTLY what not only young software engineers need to understand, but also marketing & graphic designers. It’s absurd that they’re not teaching this approach in undergrad curriculums. Great post Mark, you just won a new loyal reader! (I came from reddit)

  9. You are completely correct about needing to have domain-specific knowledge before proceeding in development.

    The same holds true for testing. You should spend some time in a program that invokes full processes including formal specification (“writing down the domain knowledge”) and formal testing practices (“creating reproducible tests based upon the encoded domain knowledge”). You begin your paragraphis on testing with “When it comes to software, we have the luxury of testing. Get your code to a usable state and then let someone use it.” This is a joke. You might as well say, “if you want to create a product for a domain, get a domain expert to start writing code for it.”

    Sorry to be so harsh, but a solid and well-developed product has many practices, and coding is only one of them.

    1. Steve – Thanks for your comment. I wasn’t really addressing automated testing. My point was that trying to build every imagined features and making everything perfect before you let a real user try it out is less of an optimal path than getting users early on.

      Was I not clear or do you disagree with that approach?

      1. Agreed! And I’m not talking about automated testing, just testing as part of the design process. Just yesterday I had a discussion with a developer about how they wanted to build an app and then release it to a test team, with the test team then designing and implementing tests. I stressed that bringing in users and test design experts during the design phase helps clarify requirements and enables the development of tests in conjunction with the development of the product.

        So I agree with you — bring in domain experts as part of the specification phase. I guess I just got taken aback by the off-the-cuff comment on testing…

        1. If it was the “luxury of testing” part that put you off, I meant in comparison to building guns where the stakes of a failed test are a bit higher. :)

  10. There is another consideration to the design of these pistols and also the match air rifles. Almost all of the manufactures are based in Germany, and Germany is the “Traditional Home” of the Olympic style air rifle and air pistol shooting, where the shooter is required by law to remove and empty the cylinder before transporting it, even in a car. This means that it requires the manometer to be fitted to the cylinder. There are designs of rifle that are mainly for sporting rather than match target shooting that have fixed cylinders to hold the air, these usually have the manometer fitted to the action block and showing underneath through the stock, so all you have to do is turn the rifle upside down, the thing is that a majority of those types are manufactured in the UK and sold in the USA where there is no law requiring the cylinder to be removed for transit in cars. This just shows that there may be more to a design than just good style, or even perceived safety. The perverse thing is that the German laws require the fitting of the manometer gauge in a possibly sub-optimal position for firearms safety, for safety reasons! But as has been said there is a lot of energy stored in a 300 bar (4350 psi) compressed air cylinder, and the German regulations for them are very strict.

  11. Gun users don’t see this as a design flaw, because they’re trained in the use of both gun and cylinder. A fair reply, and the incorporation of the round gauge in that position of the cylinder is a neat-looking piece of design.
    But the argument that we’re trained not to point the gun at ourselves, versus the device that’s inviting us to do just that, is still valid.
    The position of the gauge co-axially with the barrel is a design flaw if the gun is handled by an inexperienced person.
    That’s bit like putting wheels on the feet of ladders, with concealed brakes, and arguing that no trained ladder user would have a problem with that because they all know to apply the hidden brake before climbing.
    As for the comment that the projectile is incapable of piercing the skull…. Well, it certainly won’t do your eyeball a lot of good.

    1. Beg to disagree. This would get laughed out of the building at any gun manufacturer, weapons training or sales facility, the military, or firearms magazine. Experienced gun users would be even more opposed to this design than those who don’t understand. Experienced professionals realize that gun safety is always the first concern when dealing with ANY weapon.

      You can’t seriously be arguing that pointing a gun at your face as a requirement for operating the weapon could in any way be acceptable?

      Listen, this company went hook, line and sinker by someone who just got a product design certificate from a 18 month online art school. It looks like they hired a graphic designer to get cutesy with a gun.

      Look at the pricing of this and the company’s other weapons. There’s not a mass market manufacturer that would touch this horrible idea. That’s why the gun’s $1,500. These are one-off guns that are getting built to order.

      1. Actually Jason, Feinwerkbau is one the largest, best-established and most respected manufacturer of precision air rifles (please stop calling them weapons unless you’ve actually used one to harm another person…) and air pistols in the world. And that design of cylinder and location of manometer is the standard, used in airguns made by every ISSF manufacturer out there – Anschutz, Steyr, Hammerli, Tasco, Morini, Pardini, *everyone*, because it is the best design for the job and has evolved that way over many decades of design and test.

        And $1500 is cheap for an ISSF pistol. The Piccolo is an entry-level model. The ones you see dominating the international circuit range from €1500 to €2500 for pistols ($1900 to $3300 or more), and anything up to €4500 ($6000) for rifles. They’re precision pieces of equipment, which will happily run 500 pellets (4.5mm wide) into a one-hole group at 10m that’s no more than 8mm wide (and that’s if you use unbatched pellets and didn’t clean the airgun). These ain’t daisy or diana break-barrel squirrel-whackers.

        1. They’re great for plinking in the back yard and getting started in the sport, aren’t they? And I love my little Izh pistol as well; but for the Olympics, the standard just goes up too fast and you need kit that can cope with the demands.

        2. Also, I don’t think we’re on the same page. I’m assuming this (NOT trying to put words in your mouth), but when you referred to “gun users” were you specifically referring to higher level air rifle competition shooters? If you were, then I think we’re more on the same page than you might think.

          I was disagreeing with the idea that “gun users” (meaning the general spread of 100 million or so gun owners in the U.S.) would be comfortable or even be able to safely operate this design approach, ESPECIALLY in a pistol format. Surely a mass market consumer manufacturer wouldn’t touch a design like this? Thoughts?

        3. We’re probably talking about different demographics allright – I wouldn’t expect you’d see too many of these pistols in backyards across the US (though you might see them at the better-funded 4H and JROTC shoots, as it’s a junior’s pistol). They’d be normal across most of Europe though (yeah, they’re $1500, but the rifle I learnt to shoot on was an anschutz that was about thirty years old at the time – I was 18 – and it had been in constant, 200-rounds-a-night, 5-days-a-week use by newbies during those 30 years; and it’s still in use today at the same level, doing the same thing in the same club, nearly 18 years later, and still holding tight groups of about 16-18mm at 50m. These things *last*.)

          But also, don’t forget, mass market (and I mean *mass* market here) manufacturers don’t usually do pre-compressed air pistols, they’re a wee bit finicky for them. They tend to do springer airguns then just jump right to smallbore.

        4. How accurate are these things over longer distances? Say 300 yds or so? With a 30-06 (or something similiar) you can reach out and absolutely tag something at 800 yards (I’m talking about the capabilities of the round itself, not the gun or shooter). From what I understand, your air rifles don’t struggle in the muzzle velocity department but what kind of specs does the projectile for these rifles have? Is the rifling as extreme as a powder rifle? What’s the grain weight of the typical competition projectile?

        5. Man, the scary thing is that I remember having BB gun fights as a kid. I’m down in Mobile, AL so we’ve all been shooting since we could walk. But good God, why did our parents let us do crap like that?

        6. I don’t think they’d make it to 300 yards Jason, they’re designed specifically for the Olympic 10m event. I’ve shot mine out to 50m outdoors once for fits and giggles (on a range) and it holds about a 15mm group when there’s no wind, but the pellet is light (about 8.2 grains in a wadcutter pellet) so any wind and you could forget accuracy (but hey, it’s an airgun, it’s designed for short indoor ranges). The rifling is more extreme than a smallbore I think, 1 in 12 for Feinwerkbau’s rifles, with 12-groove rifling.

      2. Ah. I see I wrote that in a way that had unintended consequences. I was not intending to give the impression that I’m a gun user. Not one of any sort, not since my schooldays a long time ago.
        I’ll be more specific. I think this looks rather pretty, looks like a neat piece of design, until you consider the point that Mark Shead makes. At that point, you reassess. My own history with guns started with my being in the army cadet force at school, we had some pretty graphic lectures, with photographic illustrations, of what mishandled firearms could do. And the constant reminder never to be in a position to look down a barre.

      3. Ah. I see I wrote that in a way that had unintended consequences. I was not intending to give the impression that I’m a gun user. Not one of any sort, not since my schooldays a long time ago.
        I’ll be more specific. I think this looks rather pretty, looks like a neat piece of design, until you consider the point that Mark Shead makes. At that point, you reassess. My own history with guns started with my being in the army cadet force at school, we had some pretty graphic lectures, with photographic illustrations, of what mishandled firearms could do. And the constant reminder never to be in a position to look down a barrel.

  12. When my clients give short shrift to usability, I often remind them of the Florida butterfly ballot. Because of bad UI, we got eight years of George W. Bush.

    But this? This may be my new favorite visual to illustrate the point.


    1. I don’t know. You’d need to pick your audience pretty carefully. You’re going to have to deal with the “it’s actually really specifically designed for a niche case” argument whenever someone who knows what it is sees it.

  13. Easy fix.

    For all.

    Make an integrally hinged cover that shields the gauge when shooting and the muzzle when gauging. Adds a tiny amount of balanced muzzle weight but solves the problem.

    1. If you think you’re going to be tempted to look at your gauge in the middle of a match, then perhaps a bit of duct tape over the guage would ease your mind ;)

      Gotta love all the design critiques by those with no expertise in the tool or its specific application…

  14. @MARK SHEAD Why give an example of bad design in a field you are obviously not an expert in. stick to what you know chap and give bad example in your respective field?

    @Sparks well done in distracting yourself from training now refocus.. well done at Intershoot by the way.

    1. 458win, Mark’s dead on here. Find me ONE SINGLE writer or editor at a major weapons publication that wouldn’t choke on this idea.

      This a common sense issue. This isn’t questioning light trigger weights or how hot you can safely pack your loads, it’s POINTING A GUN AT YOUR FACE. Nerf wouldn’t even put a gun out that required that. Methinks doth protest too much.

      1. Jason, I’ve already explained rather carefully that nobody points a gun at their face because of this design, any more than anyone accidentally runs themselves over in their car because they tried the check the dipstick while driving down the road. You store the cylinder unscrewed and seperated from the pistol in its case; when you go to the range to shoot, you take out the cylinder, check the pressure, take it to the dive bottle, fill it, then screw it into the pistol and go shoot. The only times you have any interest in looking at the manometer are when you’re checking the cylinder at the start of the training session or match before you’ve assembled the pistol; when filling it at the dive bottle; and maybe when packing gear to get on a plane when you have to be sure the cylinder is empty. That’s it. We don’t bother checking any other time because why would we? There’s no control on that pistol for how much air pressure goes behind each pellet. If we can’t control it, and we know there’s enough air (which we know from having filled the cylinder), why on earth would we ever bother to check it, and if we did, why would we look down the barrel when you can read the gauge from 80-odd degrees off-axis anyway?

        It’s a complete and total non-issue, but having the gauge anywhere else would be a major safety issue – you can’t have a 200 bar cylinder sitting about in a cargo hold pressurised, and you can’t fill a 200 bar cylinder without a manometer, either would be a major safety hazard. (And it’s 200 for this model of pistol, but with some Walther airguns it can be as high as 300 bar).

        This really is the very best design possible, proven and tested for several decades now.

        @458 Thanks, but I have to step away from the training for a few months, Herself Indoors is expecting our first in a few weeks – Intershoot was my last hurrah for a few months :)

        1. Great post, your info clarifies a lot regarding the a typical approach/operation of these air guns.

          I have a follow up question: I know these are really high-end competition pistols & rifles, but have any of the lower end/consumer designs had the same approach?

          I now see this as being a required solution for high-spec competition, but I’m curious to know if mass-market manufacturers have been willing to reproduce the design.

        2. The lower end of the market don’t tend to use compressed air Jason, they’re like my IZH-46M, single-stroke pneumatics. You open the charging arm and then close it and it acts like a bicycle pump, compressing enough air for a single shot. No gauges on them, none needed. You do need training for them though, so that you operate the charging arm in such a way as to not point the gun along the firing line instead of at the target.

          You get some hunting airguns that don’t have the manometer there allright, but they have cylinders that you don’t remove (except at servicing, with a lot of tools). And they often don’t have regulators so you have to check the pressure during shooting as you’re tweaking how much air you bleed to the chamber for each shot. Completely different design requirements there.

  15. Many years ago my father worked at an educational software company. I once spent the day with him at his office and was promptly plunked in front of a computer to try a new game about Australia. Coincidentally, I had just finished learning about Australia in my 7th grade geography class. As I was navigating the program, I noticed that the border between Victoria and New South Wales was entirely absent. The game was in it’s final stages of testing, and no one on the entire design team knew enough about Australian geography to notice.

  16. I hope you do a follow up on the flip side of domain knowledge (which a lot of the gun fanciers are falling for). That’s constrained thinking. I had a conversation with a guy I consider to be a genius, he was telling me that we always try to use circular displays for a system because it presented all ‘threats’ as a equal distance. I stared at him not saying a word for a about 10 seconds, just looking at him with raised eyebrows. No, you make the display circular because you always made them circular that argument went out the window the first time a system was designed where the center could be moved.

  17. Could not agree more, knowing your domain is key. Its amazing how many developers jump into something without knowing a thing about it … with the ‘build it and they will come’ attitude!

  18. “I hope you do a follow up on the flip side of domain knowledge (which a lot of the gun fanciers are falling for).”

    It’s not constrained thinking, it’s domain knowledge. You’re problem I’m afraid is your lack of domain knowledge – primarily that the pistol as a pistol is far less dangerous than the 200bar pressure vessel attached to it.

    To take an analogy, you’re reasoning that the Piccolo’s design is flawed is the same reasoning that would lead someone to say there shouldn’t be number plates on the front of cars – because who in their right mind would stand in front of a 2-tonne metal box capable of 70+mph?

    But of course if the car is not running, we all walk in front of them with no compunction (parking lots, etc), and the license plate can be read off-axis without standing in front of the vehicle. And people walk in front of RUNNING cars all the time – red lights, pedestrian crossings, etc.

    This is exactly the same – anyone who springs lots of currency for a PCP Target Air Pistol will know that:

    – You don’t look at the manometer when it’s on the pistol.
    – You check it before and after shooting, when the cylinder is detached from the pistol (which in some nations is a legal requirement for storage and transport).

    A linear side scale would:
    – create a visual distraction for the shooter
    – create balance issues which would have to be countered by weighting on the other side, which increases the overall weight of the cylinder, which is so NOT the point on a JUNIOR pistol
    – create engineering challenges relating to the structural integrity of the cylinder, as the scale would have to be integral to the diameter of the cylinder (it can’t bulge out or you wouldn’t be able to unscrew it)

    Note that no dive bottles have linear scales on the side – they all use an external regulator because a side-scale would impede the engineering of the cylinder.

    Also, a side-scale would raise the risk of a novice (shooting with a club gun perhaps) turning their pistol sideways to have a look, and presenting a hazard to their neighbour. At least if you’re going to take a risk and check the dial whilst the cylinder is attached to the pistol you’re only risking your own well-being, and you’re going to damn well make sure it’s safe.

    Everything Mark Dennehy has said is spot on. This is a niche product, where it is reasonable to assume a level of basic training and compliance with the manufacturer’s documentation. It is a standard design, used across the industry without incident.
    If some other design for the manometer were reasonably viable, without making production costs prohibitive (or compromising the integrity of the pressure vessel), I suspect one of the many manufacturers would have had a crack at it by now.

  19. The author’s point about discovering the real requirements sounds like Point#1 in my Rapid Prototyping summary:
    – Start without detailed requirements.  Don’t assume you know what to build.  The customer doesn’t know exactly what he wants either.  The design process has to include direct customer interaction with the evolving prototype.  You’ll end up with a different, better product than anyone could have thought up at their desk.

  20. Indeed, domain knowledge is useful, when it’s useful. The gauge on the gas cylinder is useful WHEN REFILLING THE CYLINDER. This is a single-shot, bolt-action target pistol, not a paintball gun that might run out of propellant while in use.

  21. Hi my name is Jens and I just got may Bachelors degree in engineering. Furtermore I am shooting Air Rifels in Competition (german masters, etc.) guns like this are for olympic sport shooting and as you can see they are pretty expensive and not intendet for “fun” shooting.
    1. the gauge has to be placed there because the cartrage holds up to 300 bar pressure -> 4351 psi
    if you would mound it on the sinde the walls of the cartrage would be rediculusly thick. also it would be very heavy and not balanced anymore.
    2. you transport the gun with the cartrage losened, so that the pressure reducer has environment pressure in it. the only time I look at the gauge is when filling it and for that it is mounted on the filling tank.

  22. I am, by no means a domain expert on target pistols however this is a very interresting discussion.

    What is interresting is that Mark Shead appears to be using his experience/knowledge regarding “guns” as why this design is bad. I would not call that a mistake right away.

    Not to speak for Mark S, but it sounds like he may be similar to me in that I was taught to never point a “gun” at anyone including yourself, not matter what. So when we see this “gun shaped” device, we think we know how to use it, then wonder why in the world would you put information on the front of the gun. I would agree, domain knowledge is needed to clearly understand the whole story of this pistol.

    Relating that back to design, familarity should also be considered in the design. To anyone else, this is a “gun”. To someone that has domain knowledge on this device, would not call it a “gun”; it is a target pistol. The designer should ask themselves..”who is most likely to use this device?”, “Since it looks like a gun, should I consider the same concerns people have to guns for my design?”

    (note: I think a cap of some sort, as “mike” suggests, seems like a simple safety solution)

    While I do not disagree that it is safe to assume users familar with this device and the sport it is used in are not likely to check the gauge while the cylinder is attached, it seems that it is hard for some to not call the device a “gun” and have related safety concerns.

    It may not be the intent of this article (+comments), but I did learn a little more about “familarity” (when it can bite you) as well as the importance of domain knowledge.

  23. I shoot, I even do some air pistol.

    If I can give another analogy….

    The OP saying this is a poor place for the gauge, because a shooter might feel compelled to check it mid-match is a bit like a someone unfamiliar with cars learning where the oil dipstick is located, and saying its a poor location because it is dangerous to open the hood to check the oil while driving down the highway.

    Beyond that, it’s a single-shot pistol. The only time its hazardous is the brief time between inserting a pellet, closing the gate, and raising it to shoot. If there’s a problem, the *first* thing you do is open the gate, rendering it harmless.


    1. But keep in mind the dipstick is located specifically in a place where you cannot check it while driving down the road. Perhaps that is actually a safety feature. It makes it physically impossible (or very very hard) to do something you shouldn’t do. I would argue that the gauge does the opposite of that and makes it very easy to do something you shouldn’t do.

      But I do understand that it is a single shot pistol, you can open the gate, etc. so perhaps it isn’t as unsafe as it looks at first glance–particularly for the comment where someone thought it was a flamethrower.

  24. I would imagine that if you are charging so much for a air gun, you could design a cylindrical pressure guage that could be read from the side of the cylinder. (it wouldn’t be that hard)

  25. I often wonder if these discussions are fueled by ‘pretending to be wise’. Half of the reason I originally clicked thru was to confirm my suspicion that the original premise was incorrect. I have also noted the ‘ability to read is trumped by a desire to argue’ phenomena I have been tracking lately. The 0ther half is ironic, I look down the barrel of a pistol at least twice and sometimes several times a day. The test is, assuming anyone is still paying attention, wonders if people will keep reading and thereby gain understanding, or jump ship to degrade and/or defend such an action. Twice a day? Yes every time I holster my pistol, usually a Ruger SP 101 DAO in 357, before closing the cylinder I check to make sure the barrel is clear, by reflecting light off of my thumbnail into the barrel. This is repeated at the end of the day when I open the cylinder before bed. booga booga booga boo!!

  26. To a knowledgeable shooter, no problem.
    Looking at an angle or putting a mirror on the shooting bench solves the problem without spoiling the aesthetics of design.
    Additionally, really safe shooters put a thin, red plastic or piece of weed-whacker line through the muzzle so it shows from the open breech before handling.

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