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Comment by jaawn | Hacker News Reader

I think it might not be as bad as we imagine. All speedometers I've seen show both miles-per-hour and kilometers-per-hour, all thermostats I've seen have an option for switching to Celsius, all scales I've owned can display both pounds and kilograms (my current one even has an option for stones), all measuring cups I've seen in a long time have both systems displayed, etc. Even lumber wouldn't necessarily be a huge issue. After all, the "2 by 4" is actually 1.5" by 3.5", which equates to 38mm by 89mm. Would it be a huge deal to round that to 40mm by 90mm?

And, in any case, most people have a mobile phone now which can quickly do unit conversions. I really think it actually is feasible, if you could get the public behind it (good luck).

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You're not thinking about all the designs, tooling, manufacturing facilities, etc to build all that stuff though. That's where the real cost is.

> Would it be a huge deal to round that to 40mm by 90mm?

It actually would be a big deal to round things like that I think. Whole designs would need to be updated to take into account the new dimensions of things.

Any manufacturing component which cannot easily be adjusted to a slightly different measurement is poorly designed, in my opinion. I would expect that much of these tools could be tweaked to produce things in metric measurements. If not, the dimensions can simply be converted and re-labeled. If something manufactures a square piece of metal that is 3" by 3", is it a huge deal to just document it as being 76.2mm by 76.2mm?

> Any manufacturing component which cannot easily be adjusted to a slightly different measurement is poorly designed, in my opinion.

Imagine all of the parts in a car engine. Everything fits together perfectly. Engine mounts line up in the right places. It all has to be very precise.

Now imagine you take all those parts and round them off a bit. Nothing much, just a mm here and there. If you try to put the engine together with these parts, it's not going to work at all.

Also consider that you can't just simply convert the units. Take a 5/16" socket wrench for example. Nobody makes a 7.9375mm socket wrench.

While I think the rounding would work with lumber, I definitely don't think it would work with things like car engines. For such precisely-measured components, converting to a metric measurement with the correct significant figures should be fine.

Repair shops can maintain tools for both systems (they already have to). For converting, I mean the dimensions of a component, not tools and fasteners that need to work with tools. Those would likely take a "metric only going forward" approach.

Rounding from 38 to 40 is a difference greater than 5%. Some applications might support that, but I'm sure there are plenty that won't. For example, wood joints have very small tolerances.

> You're not thinking about all the designs, tooling, manufacturing facilities, etc to build all that stuff though. That's where the real cost is.

A lot of them are already metric.

More manufacturing is done in China, and the factories are used to the different international markets because they're often parts suppliers for foreign companies that have their designing done in various countries. So they're well equipped to make things in either inches or mm.

You're overstating it, there are only 2 other countries in the world that use imperial units

If you changed the sizes of lumber, I'm pretty sure that someone would come out with "new inch" tapes that were labeled with inches and feet but accounted for the change in size (spreading the extra millimeters out across the distance).

The dimensions in use are something that people are very used to working with and they know how to do the necessary mental arithmetic to work with them.

Luckily, the easy mental arithmetic is a main benefit of the metric system. I really doubt people would create "new inch" tapes. They would probably hang on to existing measuring tape for personal projects though.

The imperial choice of using highly composite numbers is at least as convenient for mental arithmetic as decimals.

What's 1/10th of 3 3/8"?

27/80. Asking HN seems like a roundabout way of getting the answer, though.

I-19 in southern Arizona has its distance signs in meters and kilometers as part of a test during the '70s. There have been plans to change it for a number of years but local opposition has stalled it.

https://en.wikipedia.org/wiki/Interstate_19

If I remember correctly, raw lumber here in Finland is in inches and planed lumber in millimeters :)

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