Relativity theory of clocks and rulers

Special Relativity (SR) kinematics is derived from very intuitive assumptions. Contrary to standard Einstein's derivation, no light signal is used in the construction nor it is assumed to exist. Instead we postulate the existence of two equivalence classes of physical objects: proportional clocks and proportional rulers. Simple considerations lead to Lorentz kinematics as one of three generic cases. The Lorentz case is characterized by the maximal relative speed of physical objects. The two others are the Galilean and the Euclidean cases.