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Symbol | Definition |
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≡ | exactly equal |
≈ | approximately equal to |
= | equal to |
digits | indicates that digits repeat infinitely (e.g. 8.294 369 corresponds to 8.294 369 369 369 369 …) |
The femtometre (American spelling femtometer, symbol fm derived from the Danish and Norwegian word femten, "fifteen"+Ancient Greek: μέτρον, metrοn, "unit of measurement") is an SI unit of length equal to 10−15 metres, which means a quadrillionth of one. This distance can also be called a fermi and was so named in honour of physicist Enrico Fermi, as it is a typical length-scale of nuclear physics.
A metric inch is a nickname for a preferred 1⁄4 subdivision of an ISO 2848 basic module, or 1⁄12 of a metric foot measuring 25 millimetres (0.984 in). A metric inch is 0.4 millimetres (0.016 in) shorter than an inch.
The term was similarly used to refer to the historical Soviet Bloc practice of spacing integrated circuit pins at 1⁄10 of a 25 mm "metric inch" length, instead of the western practice of 1⁄10 of an imperial inch.