Very, Very, Very Precise Time

This device is a very accurate clock in its own right. In addition, a microprocessor in the clock uses information encoded in WWV's signal to synchronize the clock with the NIST's cesium clock in Colorado. That cesium clock keeps time to within one second in 370,000 years. It's difficult to carry time from one place to another with great precision. The station's short-wave signal carries the information about what time it is, but the signal itself takes time to get from the transmitter to the receiver. It's impossible to measure the delay exactly because the signal bounces back and forth between the earth and the ionosphere. However, the delay is never more than 1/100th of a second.