  Since 1983 the meter is defined to be the "length of the path travelled by
light in vacuum during a time interval of 1/299792458 of a second". If there
was exactly one single consistent method of synchronizing clocks, or if all
corresponding methods were equivalent, one could infer from the validity of
special relativity theory on a definite value of the one-way speed of light c
in inertial frames.
  It is true that sufficiently slowly separated clocks always show middle in
time reflection when sending and receiving light signals. But a simple
consideration proves that the one-way speed of light is not a constant in
rotating systems, in principle detectable with only one clock.
  On basis of a new internal synchronization method, this also affects all
local inertial frames on rotating Earth, too, violating an absolute constancy
of the one-way speed of light. This is not a contradiction to Einstein's
original theory of relativity but to the present definition of the meter. Based
on the constant local average value c of light going there and back, however, a
modification for the definition of the meter is suggested, which would not
depend on synchronization of any distant clocks.
  Appendix: FitzGerald-Lorentz contraction and time dilation, according to
Einstein's generally accepted understanding, should be purely kinematic effects
and would not need any dynamic explanation. But an analysis of Ehrenfest's
paradox of the rotating disk shows that it is not possible to separate exactly
relativistic kinematics from dynamics. The necessity of such a fundamental
restriction is well known for a long time - though only from quantum mechanics
till now.
