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The metric bureaucrats have had to do a few strategic retreats. They tried fining grocery stores for using Imperial measures -- now, pounds and ounces can also be listed on the price sticker. We can inflate our tires in psi, as well as kilopascals (whatever they are). I've gotten used to most things metric -- but not the change from "miles per gallon" to "litres per 100 km". I want to know how far I can go on the gas I have in my tank -- not how much I need to drive 100 km.

The other thing is the meter. It started off being 1 ten millionth of the distance from a pole to the equator. A handy thing for long distance trekkers to know, I'm sure. Now it's something like the distance light travels in a vacuum in 1/299,792,458 of a second. If I'm ever in space, with a good enough stop watch, I'll be sure to check that out.

The other thing is the meter. It started off being 1 ten millionth of the distance from a pole to the equator. A handy thing for long distance trekkers to know, I'm sure. Now it's something like the distance light travels in a vacuum in 1/299,792,458 of a second. If I'm ever in space, with a good enough stop watch, I'll be sure to check that out.

Originally, the meter was designed to be one ten-millionth of a quadrant, the distance between the Equator and the North Pole. (The Earth is difficult to measure, and a small error was made in correcting for the flattening caused by the Earth's rotation. As a result, the meter is too short by about 0.013%. That's not bad for a measurement made in the 1790's.) For a long time, the meter was precisely defined as the length of an actual object, a bar kept at the International Bureau of Weights and Measures in Paris. In recent years, however, the SI base units (with one exception) have been redefined in abstract terms so they can be reproduced to any desired level of accuracy in a well-equipped laboratory. The 17th General Conference on Weights and Measures in 1983 defined the meter as that distance that makes the speed of light in a vacuum equal to exactly 299 792 458 meters per second.

These things are about precision and repeatability, not about practicality. Having a literal measuring stick for the meter locked away in a Bureau of Weights and Measures is rather primitive. Materials change with age. A bar of a metal will grow and contract with temperature. It will corrode, etc.