(i) Measurement of length: Precision measurement of length is needed to determine the inter- atomic distance is crystals in the field of crystallography.
(ii) Measurement of time: In Michelson - Morley experiment, Precision measurement of time was needed. The time interval was measured in terms of shift of the interference pattern of light. This measurement is responsible for the formulation of the theory of relativity by Einstein.
(iii) Measurement of mass: Precision measurement of mas of an atom is made by a mas spectrometer. This has verified the relation,
m =(m0√(1-v2/c2))
Where m is the mass of a particle moving with velocity v and m0 is the rest mass.