Micrometre
A micrometre (American spelling: micrometer), symbol ÃÂõm is an SI unit of length. It is defined as one millionth of a metre (1 × 10-6 m), equalivant to one thousandth of a millimetre. The letter ÃÂõ is the Greek letter mu. The micrometre is a common unit of measurement for wavelengths of infrared radiation.Some people (especially in astronomy and the semiconductor business) use the old name micron and/or the solitary symbol ÃÂõ, for the same thing, even though it is officially discouraged.
micron is also used as a unit of pressure (of a vacuum, since it is used to measure a very small pressure), an abbreviated form of micrometre of mercury (μmHg). It is equal to a millitorr, or 1/1000th of a torr.
In American English, micrometer is also the name of a tool that measures the thickness of objects.
See also: 1 E-6 m (a list of objects on the order of one to ten micrometres)
nanometre << micrometre << millimetre