Ourunitsoflinearextensionarethelengthsofmassesofmatterorthe
spacesbetweenmarksmadeonthemasses，andweassumetheselengths，or
thesespacesbetweenmarks，toremainunchangedwhilethetemperatureis
unchanged。Fromthestandard—measurepreservedatWestminster，arederived
themeasuresfortrigonometricalsurveys，forgeodesy，themeasurementof