NavList:

Lu (et al.),

You wrote:

In my ignorance, I will speculate these watches use WWVB for synchronization.

Casio's newer models can actually receive a signal from one of five transmitters. The transmitters are located in Anthorn (England), Mainflingen (Germany), Sahngqiu City (China), Fukuoka/Saga (Japan) and Fort Collins (Colorado, USA). (Actually, the watches could receive a signal from a sixth transmitter in Fukushima, Japan, but that transmitter is down because of the earthquake/tsunmai/nuclear disaster.) The maximum ranges for reception are: 1,500 km for the transmitters in Europe and China, 1,000 km for the transmitter in Japan and 3,000 km for the transmitter in the U.S. The watch selects which frequency to "listen" to based on settings made by the user.

The manual for one of my watches gives the following discalimers regarding signal reception:

-Even when the watch is within range of a transmitter, signal reception may be impossible due to the effects of geographic contours, structures, weather, the time of year, the time of day, radio interference, etc. The signal becomes weaker at distances of approximately 500 kilometers, which means that the influence of the conditions listed above becomes even greater.
-Signal reception may not be possible at the distances noted below during certain times of the year or day. Radio interference may also cause problems with reception.
Mainflingen (Germany) or Anthorn (England) transmitters: 500 kilometers
Fort Collins (United States) transmitter: 1,000 kilometers
Fukushima or Fukuoka/Saga (Japan) transmitters: 500 kilometers
Shangqiu (China) transmitter: 500 kilometers

You also wrote:

Unfortunately, I know of no simple way (short of an electronics laboratory filled with very expensive gear) to test the sensitivity of an"atomic clock" to the WWVB signal.

The Casio watches actually have a built-in feature which displays the quality of the signal being received. A blank display indicates a weak/unstable signal. An indication from "L1" to "L3" indicates the strength of a usable signal. Personally, I've experienced periods in which no usable signal could be detected. But I've also seen my watch synchronize with only a weak ("L1") signal. The manual also has this to say about reception times:

-The receive operation takes from two to seven minutes, but in some cases it can take as long as 14 minutes. Take care that you do not perform any button operation or move the watch during this time.

And finally, the manual adds the following disclaimers:

-Strong electrostatic charge can result in the wrong time setting.
-Even if a receive operation is successful, certain conditions can cause the time setting to be off by up to one second.

Perhaps this has something to do with Mark Coady's 1 second discrepancy? Just some food for thought.

Regards,

Sean C.