Hey Mike,
These are indeed a disc with a 29.5 day rotation, but this has been mounted on a larger disc hence the large moon display.
What is a Moonphase?
There are many different types of moonphase complications and their accuracy varies. Elementary moonphase complications treat the lunar cycle as if it were precisely 29.5 days. In reality, the lunar cycle lasts 29 days, 12 hours, 44 minutes, and 3 seconds. Over time, a moonphase complication operating on the assumption that the lunar cycle is a “neat” 29.5 days will accumulate errors. Those errors amount to roughly one day every 31.5 months or so. For most people, that is a sufficient level of accuracy. But for the very particular moonphase fanatic, this is not enough. Luckily for those among us, watchmakers have been striving to create ever more accurate moonphase complications ever since they first emerged in personal watches toward the end of the 19th century.
So why do most companies regard a lunar cycle as 29.5 days long? Well, simply put, it comes down to gearing. If you’ve ever seen a traditional moonphase disc, you will notice that it is adorned with two moons instead of one. Only one of these two moons is ever visible through the aperture through which the phase of the moon can be read. Meanwhile, the other moon is always traveling at the same rate, ready to take over when the other moon wanes, and it is time for the new moon to wax (which means to begin its journey towards becoming a full moon).
Those two moon phases of 29.5 days each can be tracked by a single wheel with 59 teeth. The moonphase disc is connected to the movement’s hour wheel via a series of gears that advance the disc by one tooth per day. Simple! However, as soon as the question of creating a moonphase indicator that can run without correction for long periods is raised, things get a lot more complicated.
How To Set a Moonphase Watch
As there are many different types of moonphase complications with varying degrees of accuracy and complexity, setting each mechanism to the correct phase of the moon varies. Some indications are advanced by pushers, some by the crown alone. Below, we’ll run through a general setting process that we hope will be of use to you. Please check this advice against the manufacturer’s guidelines to ensure it applies to your moonphase complication.
1. Before you set your moonphase complication, pull out the crown, and move your hands to the lower half of the dial. This removes any chance that their position could cause damage to the movement when you alter the moon disc (this is unlikely, but it is a precaution worth taking).
2. Based on the assumption your moonphase complication uses the 29.5-day model, each tooth represents one day in the lunar cycle. If your moonphase is advanced by depressing a pusher, then this is simple enough to track while setting. Use of a pusher to advance the phase of the moon is a very common method of implementing this complication, and even the Rolex Cellini Moonphase has a pusher to advance the moon disc my “one-day” increments.
3. The easiest way to set the moon phase is to check the phase of the moon online, and you can find a useful lunar tracker via a number of astronomy-related websites. Then orientate the disc so that the full moon is showing. From this point, you can easily set the moon disc accurately by referring to the moon phase online and matching the phase displayed on your watch accordingly.
4. Let’s say five days have passed since the last full moon. Orient the moon disc, so the full moon is at the top (and completely visible through the aperture). Then advance the moon disc by four days. Next, if your watch has a date, set it to one day behind the current date (yesterday). Finally, pull out the crown to the time-set position and move the hands past midnight, so the date jumps forward to today’s date. The moonphase should advance around this time to show the lunar stage five days after the full moon has passed.
https://www.bobswatches.com/rolex-blog/resources/how-to-set-moonphase-watch.html
https://watchintyme.com/index.php?t...d-how-do-you-set-it-watch-and-learn-40.19000/
Thanks for posting this one, Mike.
for posting this one up, Mike.
