Actually, the Imperial system messed itself up, post-1776. The US did screw up a bit by standardizing on the wine gallon (231 cubic inches) instead of 222 cubi

Actually, the Imperial system messed itself up, post-1776. The US did screw up a bit by standardizing on the wine gallon (231 cubic inches) instead of 222 cubic inches. This leads to a fluid ounce that is about 4% larger than an Imperial fluid ounce, and breaks the "a pint's a pound the whole world round" relationship (an Imperial fluid ounce of water weighs an ounce, and a pint of water being 16 fluid ounces is also a pound, which is 16 ounces of weight); in the US, a gallon of water now weighs "a little more" than 8 pounds. Of course, in the UK, an Imperial gallon of water now weighs exactly 10 pounds. This is because in the 1820s -- which you will note is half a century after the US and UK parted ways -- the UK decided to add more factors of 10 and 7 into their units, and redefined the pint to be 20 fluid ounces instead of 16, and a gallon became 160 instead of 128. The US and UK systems of measure diverged after 1776, and I'd argue the UK system changed more during standardization and re-standardization from the semi-formal system they shared before.