Question

do watches keep the same time

Answer 1

They should unless you go around the world once and measure two different times, one stationary and the other that went around the world, apparently the one that traveled should be off by approximately 1 nano-second from the one that was stationary.

Answer 2

Watches do not keep the same time, because the rate of their oscillation of their pendelum changes, due to different pressure applied inside the system, or due to wind or due to humidity or even due to heat. Plus, watches are constantly repaired and when that happens, does not occur at the same time to other watches, therefore from there it changes the equality of time among watches. So the best way to measure time, is using the watch made by the element Cesium-133, which is in Clorado, National Institute of Standard Te chnology, in which the watch is very effecient and it would take the next 100thousand years to repair it. They say that 1 second is calculated by the frequency of the nucleus colliding with the walls of the atom, which happens at a rate of 9192631770 times/s or Hz or tic-tacs/s.