EDIT: apparently a couple other people have already answered your questions, but I didn't see the other answers because I was typing my response. I'll leave my

EDIT: apparently a couple other people have already answered your questions, but I didn't see the other answers because I was typing my response. I'll leave my answer here cause it contains some information not in the other responses. The Wikipedia page seems to be pretty accurate. To answer your questions: > Is WWVB the norm for consumer clocks that synchronize to an outside source? If I see a clock with that feature, should I assume it uses WWVB? Is it one of several options? In the United States, yes. Clocks labeled "atomic clock" or "radio clock" are set up to sync with WWVB. Nowadays, many clocks are multi-band, which means that they are designed so that they can receive from multiple radio stations (there are a bunch of these; see https://en.wikipedia.org/wiki/Radio_clock#List_of_radio_time_signal_stations https://en.wikipedia.org/wiki/Radio_clock#List_of_radio_time...). Usually, the clock decides which station to try to sync to based on which time zone they are in (which is part of the configuration). For example, my wristwatch, a Casio AWGM100B, can receive from DCF77 (Germany, 77.5 kHz), MSF (UK, 60 kHz), WWVB (United States, 60 kHz), JJY (Japan, 40 kHz / 60 kHz), and BPC (China, 68.5 kHz). > Why not use GPS? Because of poor signal indoors? I think the main reason is that GPS is a lot more complicated, so it requires more sophisticated hardware and software (and more power) to get time via GPS. There are some higher-end watches that do use GPS - for example, the Casio GPW1000-1A. > How far does this signal from Colorado propagate? Depends on weather conditions and time of day. NIST has coverage maps that show where you can get > 100µV/m for different times of the day: http://tf.nist.gov/stations/wwvbcoverage.htm http://tf.nist.gov/stations/wwvbcoverage.htm