I have six AE-1500 watches and, about a month ago, I synchronized them all to "atomic time". According to Casio, these watches should stay accurate to plus-or-minus 30 seconds per month. After 29 days I looked at all six watches to see how accurate they were. Although they all have Casio's Module 3502 their accuracy was not exactly the same. Two of them were running a few seconds slow. The other four were running a few seconds fast. But all of them were still within plus-or-minus 30 seconds of the exact, correct "atomic time" in the end.
For a more in-depth review of the AE-1500WH and its variants, please follow this link. • FOUR Versions of the C...
The Casio AE1500 is a great value at only about $20 - $30 right now, depending on where you shop. (The list price from Casio tops out at $30.) It has a large LCD screen with the largest digits of any Casio watch I own. It would make a great watch for someone who has special needs with regard to vision. In addition to its normal timekeeping it has five alarms (one of which is a "Snooze" alarm), an hourly chime, a 24-hour countdown timer with an auto-repeat option, a 24-hour stopwatch and a Dual Time mode. The watch can be set to a 12-hour or 24-hour display for all modes. It is water resistant to 100 meters and it can run for up to 10 years on a common CR2032 lithium battery. Detailed instructions are available for download from Casio's website. Just look for module 3502.