Radio clock

Other radio controlled clocks use the time signals transmitted by dedicated transmitters in the shortwave bands.

Some timekeepers, particularly watches such as some Casio Wave Ceptors which are more likely than desk clocks to be used when travelling, can synchronise to any one of several different time signals transmitted in different regions.

The stations vary in broadcast frequency, in geographic location, and in how the signal is modulated to identify the current time.

Descriptions Many other countries can receive these signals (JJY can sometimes be received in New Zealand, Western Australia, Tasmania, Southeast Asia, parts of Western Europe and the Pacific Northwest of North America at night), but success depends on the time of day, atmospheric conditions, and interference from intervening buildings.

Their model GC-1000 "Most Accurate Clock" received shortwave time signals from radio station WWV in Fort Collins, Colorado.

It automatically switched between WWV's 5, 10, and 15 MHz frequencies to find the strongest signal as conditions changed through the day and year.

Depending upon signal strength they may require placement in a location with a relatively unobstructed path to the transmitter and need fair to good atmospheric conditions to successfully update the time.

Due to effects inherent in radio propagation and ionospheric spread and delay, GPS timing requires averaging of these phenomena over several periods.

GPS units intended primarily for time measurement as opposed to navigation can be set to assume the antenna position is fixed.

GPS clocks provide the precise time needed for synchrophasor measurement of voltage and current on the commercial power grid to determine the health of the system.

Some amateur astronomers, most notably those who time grazing lunar occultation events when the moon blocks the light from stars and planets, require the highest precision available for persons working outside large research institutions.

The Web site of the International Occultation Timing Association[32] has detailed technical information about precision timekeeping for the amateur astronomer.

Various formats listed above include a flag indicating the status of daylight saving time (DST) in the home country of the transmitter.