La Crosse Technology WS-7025U - Manual (Page 4)

4
ABOUT WWVB (Radio Controlled Time)
The NIST (National Institute of Standards and Technology—Time and Frequency
Division) WWVB radio station is located in Ft. Collins, Colorado and transmits the
exact time signal continuously throughout the United States at 60 kHz. The signal
can be received up to 2, 000 miles away through the internal antenna in the weather
station. However, due to the nature of the earth’s ionosphere, reception is very
limited during daylight hours. The weather station will search for a signal every
night when reception is best. The WWVB radio station derives its signal from the
NIST Atomic clock in Boulder, Colorado. A team of atomic physicists is
continually measuring every second, of every day, to an accuracy of ten billionths of
a second per day. These physicists have created an international standard measuring
a second as 9,192,631,770 vibrations of a Cesium-133 atom in a vacuum.