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You know, there's about 25 millimeters to the inch, and I've never seen anyone measure anything with more than 16th-inch precision for any construction job - maybe for very high-end cabinetmaking people use 32nds, but generally millimeters will give you more precision than you need, certainly if you're using a carpenter's pencil, which makes marks thicker than the smallest scale on a ruler.

I have no problem dividing things by 3 in metric. Rounding up to the next millimeter is going to result in an error equivalent to a couple of human hairs. If I'm working with wood and I need a perfect fit I'm going to be using sandpaper long before that.

Seriously, do you imagine that construction workers and craftsmen in Europe, Japan and the rest of the world spend their days ina state of helpless anxiety because of their inability to divide things with sufficient precision, or do you think they just get on with it and make buildings and furniture as good as any you can find in the US? The construction industry didn't collapse in the UK, Ireland, or Australia when they adopted the metric system.

No, I assumed they had a very good way of doing it, which is why I asked about it :-) It was a sincere request for comment but it obviously came off as a cynical challenge, which wasn't my intention.

> I would love to hear from someone who does carpentry (or some craft-like equivalent) with the metric system- specifically what kind of ruler/tape they use and whether it has a special 1/3 and 2/3 mark on it (since you don't want to have to eyeball 0.33333....) or if they just avoid dividing things by three altogether.

I would love to hear from someone that uses the imperial system how they determine exactly 1/3 of 10 inches and how they eyeball 1/3 of 5/6 of an inch.... My point is it is easy to find measurement scenarios that would make life a little harder for either system. 12cm (metric) for example is trivial to divide into 1/3, 2/3, 1/2, 1/4, 1/6 etc etc. 4.72 inches (imperial equivalent of 12cm) would be harder to do.

Besides there are very easy geometric methods to divide a line exactly into any number of equal parts, even if you do not know its actual length precisely.

I've done a bit of carpentry around my house. Since I live in Sweden I always use the metric system.

For me the focus on division by three is a bit strange. Sure I sometimes need to divide by three, but I also need to divide by five, or two or seven. I guess the thing is that our building standards are expressed in the metric system, so it makes sense thinking about them in terms of meters or centimeters. US building standards are expressed in the imperial system, so it makes sense to think about them in feet and inches.

Why would I want a unit that's 1/60th of a meter when I have a perfect 1/100th of a meter? A third of a meter is 33.3cm, working with wood you don't need more precision than that, if the decimal sign makes it difficult to do calculations, just step it up to 333mm.

I'm not a carpenter by trade but I guess that a professional carpenter here learns quite well how to divide by three even in metric. I see this argument popup every time there's a discussion about using the metric system in the US and I find it weak. For me this argument only sounds like "but it's hard to learn something new".

I'm sure there are pros and cons with both the metric and the imperial system, but in the globalized world we live in, the fact that The Rest Of The World uses the metric system should be a pretty convincing argument to use it in the US as well. I mean after all, The Rest Of The World has accepted English (in one form or the other) as the Lingua Franca in order to make communication across borders easier. You don't see us whine about stuff like "but in Swedish I can much more succinctly express that it's my paternal or maternal grandparent I'm talking about, so I don't want to use English".

Point taken, and I acknowledged in my first comment that it was a weak reason compared to the reasons for adopting. It wasn't meant as advocacy :-)

I would point out however that no one (that I know of) claims that English is the most popular because it is intrinsically the most efficient for all situations- i.e., on its merits as an efficient language rather than geopolitical factors. I definitely think that there are certain situations where communicating using non-English would be (locally) optimal- even if the parties communicating were fluent in English. Even as a native English speaker I truly wish English had the equivalent of the Tagalog particle "daw/raw," for example ( http://tagaloglang.com/Tagalog-English-Dictionary/English-Tr... ), or the fact that Cantonese can often communicate the same information as English using far fewer syllables...

In other words, I'm perfectly fine saying that using English is globally optimal (and convenient for me) because of its adoption, while still being perfectly happy knowing that some languages have attributes that make them more efficient, if you know them, in certain circumstances. I don't pretend ex-facto that English got this way because it is a truly superior solution in all circumstances if only everyone knew it. Nor do I feel like English's status as a (quasi)-standard is threatened by someone pointing out that Swedish would be more efficient in some settings (say, family history) even if everyone did know English. I would say "cool."

Defining units in terms of other units via something other than base-10 scaling in order to have more integer factors than 2 and 5- in some cases trading the 5 for 3 and 4- can be advantageous. That's all I'm saying, nothing more or less :-)

When i was building stuff out of timber i would typically only work in mm (or metres for longer lengths (timber is sold in full lenths of 6 metres or shorter bits at various lengths (at least in .au)) and don't need any further precision.

a 334 mm length will quite happily go in a 333mm gap. though again i'm not a professional carpenter i just worked with my father a lot.