The unit of time measurement is the same among all nations. Practically
it is 1-86400 of the mean solar day, but really it is a perfectly
arbitrary unit, as the length of the mean solar day is not constant for
any two periods of time. There is no constant natural unit of time.
Time measures are used in telling the time of day, in problems in
longitude and time, in figuring interest on notes and bills, and in
numerous other ways.