I once worked in the quality control department of a factory. There were all kinds of interesting tools for testing different things. One of them was to electronically test the thickness of anodizing. We had a lot of tools that would measure to 0.001”, but the anodizing tool divided each 0.001” one-thousand times. It measured how many millionths of an inch the anodizing was. We call them “mils” (for millionths) even though that was not technically correct.