Fascinating rulers from London, Frankfurt and Germany. While the other side is identical, meaning a centimeter is still a centimeter, this photo reveals an oddity of math and engineering. The size of an inch was variable at one time! This changed in 1959.MI
Thanks Horst for pulling these relics out and giving these Americans a lesson on our silly units of measure. For more, go here:
https://en.m.wikipedia.org/wiki/Inch
https://en.m.wikipedia.org/wiki/Inch