Non-Invariant Velocity of Light and Clock Synchronisation in Accelerated   Systems
  Clock synchronisation is conventional when inertial systems are involved. This statement is no longer true in accelerated systems. A demonstration is given in the case of a rotating platform. We conclude that theories based on the Einstein's clock synchronisation procedure are unable to explain, for example, the Sagnac effect on the platform. Implications on very precise clock synchronisation on earth are discussed. 
Fran\c{c}ois Goy