  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.
