Comments by "ke6gwf - Ben Blackburn" (@ke6gwf) on "US Auto Industry"
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@ΑΡΗΣΚΟΡΝΑΡΑΚΗΣ that's not an accurate claim lol
Long ago there was a piece of metal used to calibrate all measurements in the US, and one in France.
They both were constantly changing length slightly, and so the units were constantly diverging, so it was decided to use the more stable one as the reference for both.
So the US Customary system length units was based off the French Prototype, thus keeping it stable in relation to the Metric system, and so now we have a precise conversion factor between the two.
Since then however, both USC and metric are based off the speed of light, and various other Constants, so you can't even say that it's based off a piece of metal.
In any case, USC isn't, and never was, based on metric units.
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@ΑΡΗΣΚΟΡΝΑΡΑΚΗΣ nope, that's not correct.
An inch equals 25.4 mm, just as 25.4 mm equals an inch.
It's just two fixed points on a conversation chart, and the inch is no more defined by the mm than the degree F is defined by the Degree C, or how the distance to the moon can be measured in light years or metres.
The relationship between the inch and the mm was arrived at by comparing the two standards, measuring the master Yardstick with the Prototype Meter, and then measuring the Prototype Meter with the Master Yardstick, and they found the relationship between the two, and then locked the relationship to what it was that day (since the masters were always changing)
There was also a later adjustment made because the Imperial inch and the US Customary inch had diverged slightly, and so the US and the UK both shifted their inch slightly towards each other and met in the middle, which is how it arrived at 25.4, when it has previously had more decimals.
But that was done by the US and UK, not the SI, because the US is who defines the length of the inch, which is now based on the time light takes to travel in a vacuum, because the old metre prototype was too unreliable, constantly changing length.
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