A transmitter call can be made manually, but the minutes and seconds never need to be adjusted. The liquid crystal display indicates month, date and time zone as well as reception information. From sundials to clepsydrae to hourglasses to mechanical clocks to pendulum regulators to electric clocks to quartz mechanisms to massive orbiting telescopes looking back almost to the Big Bang the improvements have been incremental and accelerated. Junghans MEGA radio controlled watch, gold finish. Atomic clocks use cesium 133, a metal isotope that resembles mercury, to measure time.
Detectors count the vibrations of the atoms in the vacuum.
By international agreement physicists have determined one second as 9,192,631,770 vibrations or cycles of the cesium. In Boulder the NIST actually has 24 atomic clocks, whose results are averaged to determine a second. This atomic tick tock is fed into computers at NIST and regulates the WWVB radio transmitter located in Fort Collins, CO, where the exact time signal is continuously broadcast throughout North America with 23 kilowatts of radiated power at 60 kilohertz wavelength. The longwave radio paths found at that low frequency are stable and can use the earth and ionosphere as a wave guide to follow the curvature of the Earth for long distances. Junghans MEGA radio controlled watches, shown in titanium, gold, and stainless steel.