An inertial clock present at two events always measures a shorter time than a pair of synchronized clocks in any inertial reference frame would register between the same two events (as long as the events don't occur at the same place in that frame).

Question

Quizplus · Accepted Answer

According to the theory of relativity, an inertial clock moving between two events measures the proper time, which is the shortest time interval compared to any other clocks in different inertial frames that are not at rest relative to the events.

An Inertial Clock Present at Two Events Always Measures a Shorter