by Guest » Sat Nov 10, 2007 1:24 am
The Greek letter mu (µ) is used as the symbol for the prefix micro-, that is, 10^(-6). It should not be used standalone as a unit of length, but this misuse is pretty common. I assume they really mean micrometers, µm.
Since 1" = 25.4 mm, it also equals 25400 µm.