And still: do fast-moving scales contract or elongate?

Traditional definition of the length of fast moving scale and the concept of relativistic length (CRL) are considered from the point of view of condition of relativistic covariance. It is shown that the last consept satisfies this condition, whereas the traditional definition is in contrast with it (''synchronous length'' is not a 4-vector). It is noted that following from CRL ''elongation formula'' corresponds to the growth of formation length of fast hadrons with energy. It is difficult to adjust the last fact with the traditional opinion of the tendency to zero of longitudinal dimensions of relativistic particles. It is stressed that additional account made of the influence of Earth's motion on the velocity of light propagation along transverse interferometer arm in the known inperpretation of the Michelson-Morley experiment leads to the ''elongation formula'' for a longitudinal arm