In the nineteenth century, the introduction of standard time and time zones divorced the "time of day" from local mean solar time and any links to astronomy. Time signals, like the bells and dials of public clocks, once were relatively local affairs; the ball that is dropped in Times Square on New Year's Eve in New York City once served as a time signal whose original purpose was for navigators to check their marine chronometers. However, when the railroads began running trains on complex schedules, keeping a schedule that could be followed over distances of hundreds of miles required synchronization on a scale not attempted before. Telegraphy and later shortwave radio were used to broadcast time signals from the most accurate clocks available. Radio and television broadcasting schedules created a further impetus to regiment everyone's clock so that they all told the same time within a very small tolerance; the broadcasting of time announcements over radio and television enabled all the households in their audience to get in synch with the clocks at the network.