Protophysics and Special Theory of Relativity. First, a proposal for a constructive foundation of the Special Theory of Relativity by M. Buth is criticized and confronted with an alternative proposal by the author. The main idea is to solve the problem of transforming coordinates between inertial systems in terms of the General Theory of Measurement. Regarding transformations of co-ordinates as transformations of thecorresponding “functions of measurement” these functions have to meet two demands. 1. To identify measured values which are related (...) to different inertial systems and measuring procedures as the same magnitude, the ratio scale of length and duration has to be defined with respect to the whole class of inertial systems. 2. Using the concept of a certain physical magnitude, propositions about measuring devices are made which are invariant with respect to measuring procedures. As aconsequence every transformation between functions of measurement has to be an equivalence relation. The first demand leads to linearity, the second one reduces the set of permissible transformations between inertial systems to the alternative of Galilei- and Lorentz-transformation. The (im)possibility of putting an absolute simultaneity into practice decides between these transformations. (shrink)