Who Told Your Clock to Fall Back?

When daylight saving time ends, some clocks fall back an hour without anyone touching them. In the U.S., “atomic” wall clocks and watches are really quartz clocks with a tiny radio inside, tuned to NIST radio station WWVB near Fort Collins, Colorado. WWVB sends a slow 60 kHz time code, one bit per second, and that code includes a daylight saving time flag. NIST’s own guide even notes that some analog clocks may have to spin forward 11 hours, because their hands can’t move backward.

Sources:
– NIST, Radio Station WWVB:
– NIST, Help with WWVB Radio Controlled Clocks (incl. coverage maps):
– NIST Special Publication 960-14, WWVB Radio Controlled Clocks: Recommended Practices for Manufacturers and Consumers (2009), Sec. 6 and 6.A:

Notes: Clock photos are illustrative. Two of them (the opened clock and the black wall clock) are European radio clocks tuned to Germany’s DCF77 signal, which work on the same principle. The gear photo is a 1971 quartz clock movement, not a radio clock. The coverage maps are NIST simulations.

Image credits (Wikimedia Commons unless noted):
– Analog atomic clock – ECTran71, CC BY-SA 4.0:
– WWVB from helicopter – Allen Turner, CC BY-SA 3.0:
– WWVB Towers – NIST, public domain:
– NIST-F2 cesium fountain atomic clock – NIST, public domain:
– Inside radio clock – Harry20 at German Wikipedia, CC BY-SA 3.0:
– WWVB coverage maps (0600 and 1800 UTC) – NIST, U.S. Government work:
– Oregon Scientific RM338P – Morn, CC BY-SA 4.0:
– Clock on the wall – Kacper Perschke, CC BY 3.0:
– Quarzuhrwerk CQ 2000 – Deutsches-uhrenmuseum, CC BY-SA 4.0:
– WWV transmitter building – Glenn Nelson, NIST, public domain:
Images were cropped, scaled and panned. CC BY-SA images are used under their licenses ( , ,

Narration: AI voice (Microsoft neural TTS). Graphics: Oddly Useful Dude.

#Shorts #DaylightSavingTime #FallBack #HowItWorks #OddlyUsefulDude

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