| Definition: | for a rigid rod, three-dimensional distance between begin A and end B of that rod measured in some inertial frame S synchronously, i.e., in the same local times tA=tB of S
Note 1 to entry: The local length d of a rod in a frame S depends on the choice of S. In other frame S′, the local length d′ of the same rod may be else because measuring position of its begin and end being synchronous with respect to S may be not synchronous with respect to S′.
Note 2 to entry: The coherent SI unit of local length is metre, m.
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