Smile . Just the other day I was reviewing calcs where a Ph.D. Engineer had converted units of natural gas flow from MMBTU/hr to MMSCFD. He had used published numbers for the conversion. He forgot that published numbers are for a typical composition of gas and not for the gas under consideration that had a high percent of ethane in it !!
So yes - any engineer can do the conversion. But not all conversions are correct.
Hey, yeah, you’re right. We kind of ran with it, but the OP seems to be more about what rounding does to the final result when using one or the other system.
Perhaps there is a tendency for one or the other unit system to lead to a chunkier mechanical design? This is going to sound silly, but I think of SI components as being smaller than Imperial components. Dimensions that take few digits to express tend to get favored, and these land at different physical lengths in the two systems. Maybe this is just random, but it keeps looking to me like the SI devices wind up smaller. Of course, this might represent cultural trends and where things were made - for example, at least a few decades back, American cars had Imperial dimensions and were also very big, compared to European.
In my garage I have four sets of spanners (wrenches) and some taps and dies. I have Whitworth, BSA and metric, and a different set for bicycles. I never understood how two totally different sized spanners could be stamped with the same dimension. Many, of course are pretty interchangeable.
I imagine that many people in America have the same. The difference is that, in my case, only the metric sizes have seen any use in the last two decades.
With residential construction it is not much of an issue. In Calgary building permits require plans to be submitted in metric but we use US sized materials and and measurements for residential construction. I expect its the same in every Canadian city since we are officially metric. Most large measurements are going to be some multiple of 610mm which is Canadian Bureaucratic for 2’.
Considerate designers either produce plans with key measurements in American units, or converted plans for the jobsite. Its common for the scale to be 1:48, then 1/4" is equal to 1’ and you do not even need a scale ruler. If the plan has been resized it will have a ‘do not scale’ stamp, in which case you find a couple of conveniently round measurements to calibrate to. Its still easy enough if it is all in metric.
Ultimately it is all relatively simple due to a few issues:
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Conversion errors are well below tolerances required for key measurements. The difference between 1/16" and and 1 mm is insignificant on the scales being worked with. 1220mm is so close to 4’ it just doesn’t matter. The materials being used in rough construction are just too course for anything less than 1/16" to be significant. Framers usually don’t measure anything to more precision than 1/8".[/ul]
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An American Unit scale ruler works just fine on a metric unit plan and vice versa
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Length units are just numbers on a tape measure. Give me a metric tape or an American unit tape or even a Martian tape, I don’t care as long as the units are the same as on the plan or measured off the plan to scale.
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I picked up a cheap set of ‘universal’ sockets a while back that are just excellent, and work very well for most situations on either SAE or metric. If I am worried about a particularly tight nut I will look for a precise fitting socket of good quality to avoid rounding but they are just as good as dedicated sockets of ordinary quality.