La Crosse Technology Intelligent Weather Station WS-9020U 915MHZ - Manual (Page 6)

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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 and date 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 intelligent
weather station. However, due to the nature of the Earth’s Ionosphere,
reception is very limited during daylight hours. The intelligent 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. For more information on the atomic clock and WWVB
please see the NIST website at
http://www.boulder.nist.gov/timefreq/stations/wwvb.htm.
FUNCTION KEYS
Intelligent weather station:
The intelligent weather station has 5 easy to use function keys on the
right side of the unit.
SET key
MAX/+ key
CH key
MIN/- key
ALARM key