Chapter 29.2, Problem 2EYU

Two identical atomic clocks are manufactured at a factory. One clock remains at the factory, and the other is transported across the country to a physics lab. When the clock arrives at the physics lab it reads 9:00 A M. At this same time, does the clock at the factory read a time that is before 9:00 A M., equal to 9:00 A M., or after 9:00 A M.? Explain.