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A micrometer is a measurement device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades. The first micrometer was developed by Jean Laurent Palmer of Paris in 1848.
A petametre (American spelling: petameter, symbol: Pm) is a unit of length equal to 10^15 metres. âºâº Definition: Micrometer A micrometre (American spelling: micrometer, symbol Âµm) is an SI unit of length equal to one millionth of a metre, or about a tenth of the size of a droplet of mist or fog. It is also commonly known as a micron, although that term is officially outdated. It can be written in the expanded mathmatical notation (1Ã10-6 m)