Two observers, moving with respect to each other, who each construct identical clocks in their respective IFRs, will determine that the other’s clock is running at the same rate as their own. This can be accomplished by each observer sending a radio signal based on the frequency of its clock to the other observer. After accounting for motion induced Doppler in the received signal, each observer will conclude that the initial rate of the other’s clock is the same as their own.
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