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Features:

• Accurate to 1second per million years
• Sets automatically to WWVB radio signal (manual setting is also possible)
• 12/24 hour time display (hour, minute, second)
• Alarm setting with snooze function
• Calendar display with weekdays in your choice of three languages (English, French, Spanish)
• Time zone setting (13 available)
• Daylight saving time ON/OFF option
• Moon phase display (8 phases total)
• Indoor temperature display in either °F or °C
• Electro-luminescent backlight, by push button, for 3 seconds
• Integral base for table/shelf/desktop placement
• Powered by two AA alkaline batteries (not included), with normal life of about 1 year

Specifications:

• Indoor temperature measuring range:
  32° to 122°F with 0.2°F resolution
  (0° to 50°C with 0.1°C resolution)
• Temperature checking interval:
  Every 10 seconds
• Dimensions:
  4.64 inches (11.8cm) wide
  3.93 inches (10cm) high
  1.85 inches (4.7cm) deep (including base)

The NIST (National Institute of Standards and Technology, Time and Frequency Division) maintains a radio station, WWVB, in Ft. Collins, Colorado. 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.

WWVB (the station’s identification just like any other radio station) continuously broadcasts time and frequency signals at 60 kHz. The carrier frequency provides a stable frequency reference traceable to the national standard. There are no voice announcements on the station, but a time code is synchronized with the 60 kHz carrier and is broadcast continuously at a rate of 1 bit per second using pulse width modulation. The time code contains the year, day of year, hour, minute, second, and flags that indicate the status of Daylight Saving Time, leap years, and leap seconds.

The La Crosse Technology WS-8055U Radio Controlled Moon Phase Alarm Clock:

The La Crosse Technology Radio Controlled Moon Phase Alarm Clock maintains its incredible accuracy by automatically tuning into the WWVB radio signal. The built-in antenna ensures reliable signal reception up to 2000 miles (3200km) from the WWVB transmitter. As a result, the La Crosse Technology clock will calibrate to the atomic clock not only throughout the mainland U.S. but also in much of Canada. You need only insert the batteries, wait until the signal is received, and program the desired additional settings. In locations outside of WWVB range, the La Crosse clock can be manually set and will provide the high degree of accuracy of any quality quartz clock.

In a nutshell, here's how the the La Crosse clock works: The clock's antenna is specifically tuned for optimal reception of the 60 kHz time signal. The time signal received on the antenna is demodulated by an onboard receiver, which sends the information to the clock's CMOS microprocessor for decoding. Once your clock has automatically set its time for the first time, it ensures continuing accuracy by automatically tuning into the WWVB radio signal once per day at midnight. (If no signal is detected, the clock performs its WWVB check hourly until the signal is found.) As long as your clock is kept within transmitter range, it will continue to display the absolutely precise time, automatically adjusting for summer time/winter time changeovers if the daylight savings time option is ON. Should you move your clock out of transmitter range for an extended period of time, the clock will continue to operate as a highly accurate quartz-controlled clock. Upon re-entering the transmitter range, your clock will correct itself again to the precise WWVB time signal.

This unit does not come with batteries.  It requires 2 AA batteries  which may be purchased below.