I have a number of analog watches that run on button batteries. The batteries run down, get replaced, and then I have to reset the time and date. I remember the original instructions they all came with about setting the date outside the range of roughly 9:00 PM to 3:00 AM, but I always have a 50:50 chance of the date subsequently changing at noon instead of midnight. I've tried setting the date at all hours of the day, but nothing changes my odds. Is there some trick to ensure that the date changes at midnight after setting it?
The problem is that you know what time of day it is when you set the watch, but the watch doesn't. The trick is to do it in reverse and let the date be the basis for the time of day. It's a three-step process. In most cases the watch stem has three positions: all the way out to adjust the time, half way out to adjust the date, and all the way in to disengage the stem.
The window of 9:00 PM - 3:00 AM when you aren't supposed to set the date actually has nothing to do with defining the date change trigger. It's to avoid damaging the gears that drive the date change. So the first step is to set the time on the watch to anything outside that range and then push the stem closed. That avoids potential damage when setting the date.
Pull the stem halfway out and set the date to yesterday's date, and push the stem back in.
Pull the stem all the way out and start moving the time forward. As you approach 12:00, the date will start to change, but it might be on the first time you approach 12:00 or the second. When you hit 12:00 and the date changes, the watch is at 12:00 AM, the start of today, with today's date. From that point set today's actual time. If it is past noon, make a full circuit past 12:00 again and then set the time.
The hour hand on your watch passes 12 twice a day. On only one of these passes will you see a change in the date showing in the date window. You can hence know whether your watch is showing an AM or a PM time by pulling the crown out whatever number of notches allows you to set the time, then wind the watch forwards (backwards may cause issues) until the time passes 12.
- If the date window changed, then the time the watch now shows (e.g. 1 o'clock) is in the morning (1 am).
- If the date window didn't change, then the time the watch currently shows is a PM time
Now you know whether the watch is showing an AM or PM time you can adjust the time accordingly
- If the actual time of day is 6am, wind the watch forwards 5 hours til it reads 6 o'clock.
- If the actual time of day is 3pm, wind the watch forwards 14 hours (so it passes 12 again) and reads 3 o'clock.
If you determined that your watch was showing AM, and it's actually 3pm but you only wind the watch forwards 2 hours (so it reads 3 o'clock) then the watch will effectively be showing 3am and it will change the date at midday tomorrow instead of midnight tonight.
Finally, set the date by pulling the crown out whatever number of notches engages date setting mode.