micrometer

noun

1. A device used to measure distance very precisely but within a limited range, especially depth, thickness, and diameter.
2. (US, alt-of)US spelling of micrometre (“one-millionth of a metre”).

   “A strain is usually expressed in μm/m (micrometer per meter), also known as microstrain, which has the symbol µε. You may also see “mV/V,” which refers to the output in millivolts per volt of excitation.”