this post was submitted on 05 Feb 2025
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I have to say that I do this professionally. There is no reason at all to specify tolerances like that. You very much should use at least centimeters with the +/- in decimals. This is the whole point of the metric system. And it aggravates me. We are not stupid as manufacturers. It is very simple division. I am American and have to deal with German and Japanese tolerances quite literally every day. Sure, there are different required ISO tolerances based on millimeters, but as far as prints go? Every company usually specifies their own tolerances. Complying with ISO mostly means that you understand what they require overall. It is my professional opinion that not using the breadth of the metric system is absolutely absurd.
Every professional that deals with stuff that needs around 1mm precision uses mm. Metal roofing, gutters, any machining, etc. It is to prevent ambiguity. I used to build roofs and for like wooden beams we used meters and cm, but that was because a couple mm here and there rarely ever mattered. All in all using mm is usually the best choice.
What professional area? Because I don't recall ever seeing listings of thousands of mm.
Metal roofing thing (idk how to translate, am not british) are always in mm. We would buy them at like 5 meters long and measure for cutting using mm. https://limarija-sebastijan.hr/krovni-zidni-i-ostali-profilirani-limovi/trapezni-lim/ All the drawings for metal things are in mm. What is not is like diameter of the pipes. The store I linked sells rolls of sheet metal (again don't know how to translate) in cm, but all the other stores sell in mm. https://olx.ba/artikal/19038696/lim-u-rolni/# When you want custom bent stuff (like the metal.. things that go on the sides, or custom gutters) you make a drawing in mm (can't explain, but I'l draw one if you want).
I just said "professional" because the one I replied said it, without saying what profession. Roofing is a profession, and metal roofing stuff doing (again don't know how to translate) is also a profession.
And all the schematics I have seen for metal parts, and in cad software in general, is in mm. Tailoring is also in mm (https://tehnicki.lzmk.hr/clanak/kroj).
Maybe it is a US vs rest of the world thing ? Maybe I'm not expirienced enough to make such sweeping statements.
Again, you put thousands of mm because mixing cm and mm (and m) can lead to mistakes. I even remember cutting wrong because I heard like 2570 instead of 2507 (he's up there measuring, while I'm down cutting).
House blueprints are usually in meters. Window sizes are in cm.