My original name for this topic was “That’s insane” but that description only applies to a piece of the discussion. I have long held the position that the US should switch to the metric system for measurements, not because it’s necessarily better than imperial units but because it would be a lot easier if we followed the same standard as everyone else.
The bizarre part of this debate is that the US passed a metrication law in 1975 but, because it was voluntary, most of the switch never took place. Standards usually require more push than that, since there is some time, effort, and cost involved in switching. As a result, we have a bizarre hybrid, where some metric units are used, a lot of imperial units are used, and we have the occasional inevitable failure. The picture above is a standard international meter bar made of platinum-iridium alloy, which was used as the basis for US measurements in feet from 1893 to 1960.
That bar, and the measurement it represents, is where this story switches from annoying to ludicrous. The US standard foot, known as the “survey foot” was based on that bar. In 1959, the US switched to the “international foot”, which is 0.0002% shorter. The international foot is slightly easier to relate to the length of a standard meter; in ordinary life, the two feet are indistinguishable. However, if you use the international foot for long distances measured with the survey foot (or its predecessors), there will be real discrepancies. The obvious question is why not switch to the metric system, as we should have 100 years ago, rather than tinker with imperial units.
Again, the argument that the metric system is more logical has some flaws. For example, the meter was originally defined as one ten-millionth of the distance between the north pole and the equator, on the longitude of Paris. Specifying the north pole and Paris is important, as the earth is not a sphere; measuring from the south pole to the equator or measuring on a different longitude would give a slightly different meter length. The modern standard for a meter avoids this issue by being tied to a natural standard: a meter is 1/299,792,458 of a light-second. Of course, that lacks the simplicity of 1/10,000,000 and is also tied to the second, which is an arbitrary length of time.
In short, all our units are made up. If we were starting from scratch today – a terrible idea – maybe it would make sense to set the length of a meter as 1/300,000,000 of a light-second. But we’re not. It literally doesn’t matter: we could set the standard meter at 40 US survey inches and the metric system would survive, with all the units made slightly smaller. The world, the universe, exists, and we make up units of measurement to describe it; switching from one system of units to another does not change the physical reality, only what numbers we put in front of the units. Maybe the fact that the metric system is based entirely on powers of ten makes it easier; maybe there’s something to be said for using fractions in daily life rather. Who cares, as long as we understand that (a) there’s nothing inevitable about any system and (b) having two different length feet is insane.