A 1-2” Etalon indicating micrometer. Used mostly for quality control, the guy that most machinists loathe. .00005” resolution (that’s fifty MILLIONTHS of an inch) A human hair, depending on from where it was plucked, is about .002-.005” thick. A sheet of cheap copy paper is .002” thick. This thing measures two orders of magnitude more accurately than that. Pretty much down to individual layers of atoms at this point.