Operationalization of Relativistic Motion
  We demonstrate the definition of basic observables from physical operations, the key to overcome hidden stumbling blocks and apparent paradoxes from unscrutinized (classical) formalisms. We develop Helmholtz program of basic measurements for relativistic motion. We define the basic observables by direct comparison: "longer than" if one object or process covers the other. To express the spatiotemporal order also numerically (how many times longer) we cover them by a locally regular grid of light clocks. These are the basic physical operations. From their interrelation we derive mathematical relations, e.g. for different observers the formal Lorentz transformation; for accelerating observers we reveal a measurement-methodical view on the apparent Twin paradox. 
Bruno Hartmann
gr-qc physics.hist-ph