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The millimetre (International spelling as used by the International Bureau of Weights and Measures; SI unit symbol mm) or millimeter (American spelling) is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length. Therefore there are thousand millimetres in a metre. There are ten millimetres in a centimetre.
Petameter or petametre is equal to 1015 meters (unit of length), comes from a combination of the metric prefix peta (P) and the SI unit of length meter (m). Plural name is petameters.