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GPS satellite navigation receivers also internally generate accurate time information from the satellite signals.
Dedicated GPS timing receivers are accurate to better than 1 microsecond; however, general-purpose or consumer grade GPS may have an offset of up to one second between the internally calculated time, which is much more accurate than 1 second, and the time displayed on the screen.
Other radio controlled clocks use the time signals transmitted by dedicated transmitters in the shortwave bands.
Systems using dedicated time signal stations can achieve accuracy of a few tens of milliseconds.
One common style of radio-controlled clock uses time signals transmitted by dedicated terrestrial longwave radio transmitters, which emit a time code that can be demodulated and displayed by the radio controlled clock.
The radio controlled clock will contain an accurate time base oscillator to maintain timekeeping if the radio signal is momentarily unavailable.
One of the first radio clocks was offered by Heathkit in late 1983.
The timekeeping between updates was thus considerably more accurate than the crystal alone could have achieved.Inexpensive clocks keep track of the time between updates, or in their absence, with a non-disciplined quartz-crystal clock, with the accuracy typical of non-radio-controlled quartz timepieces.