"External" clock synchronization and sbsolute motion The “external” clock synchronization goes as follows: Consider that the clocks C(x) located at the points M(x) of the OX axis of I inertial reference frame read all zero (t=0) as a result of a standard (Einstein) clock synchronization procedure. Let C’ be the wrist watch of an observer R’ who moves with constant speed V in the positive direction of the OX axis. Clock C’ is adjusted to read t’=0 when it passes in front of a clock C(x) reading zero as well. The trip of clock C’ lasts dt’ when measured by R’ being a proper time interval but lasts dt when measured by observers from I being a coordinate time interval. The two time intervals are related by the time dilation formula dt’=dt/g (1) g representing the Lorentz factor. Equation (1) enables R’ to find out his speed knowing dt and dt’. Knowing that the relativity principle could be stated as: “All physical laws are the same in any inertial reference frame, no inertial reference frame is privileged i.e. distinguishable from the others by means of “internal” empirical evidences” we could say that (1) is an experiment in which the moving observer R’ is not “confined” in his rest frame and so it is out of the requirements of the relativity principle. The way in which the reference frames are chosen is arbitrary. Is there some error above?