On November 18, 1883, four standard time zones for the continental U.S.A. were introduced at the instigation of the railroads. At noon on this day the U.S. Naval Observatory changed its telegraphic signals to correspond to the change. Until the invention of the railway, it took such a long time to get from one place to another that local "sun time" could be used. When traveling to the east or to the west, a person would have to change his or her watch by one minute every twelve miles.