How should you set the moon phase???

I have a JLC Master Calendar and setting the moon phase gives me some challenge.

As I like to obtain precision and prefere that the moon phase on my watch is correct I have following issues:

The moon disk on the cal. 924 has 59 teeth and there are two moons on the disk. This result in that one moon can be totally in center in the moon phase display and the other moon on the disk can be just before center and just after center.



I would like the moon on the moon disk to be in center if the full moon is during the day (from 06:00 to 18:00). If the full moon is during the night (from 18:00 to 06:00) I would like the moon on the moon disk to be just before center the day up to the full moon and just after center the day after full moon.

This gives me some challenge how to set the moon phase on my watch (the moon disk). I have made this table to see my options:


First colomn is the days/teeth on the moon disk
Yellow = Full moon and the time indicated is the correct time of full moon i Denmark

It is clear that my watch will not meet my desired accuracy. When inspecting the table it seems that a correction of the moon disk by + one day the 14 February 2014 would be the right thing to do. However the imprecision seems to adapt to the normal from the 25 November 2015. As my moon calendar does not go beyond the year 2015 this is not clear. The three dates: 3 July, 31 August and 30 October all in 2012 can be accepted that the moon disk in one day early.

It would be so nice to have a watch like the Atmos Phases de lune with an accurate moon disk. The moon phase model loses only one day every 3821 years.

All the best
Ados

I do like your post very much, as it demonstrates that sometimes, OK is not good enough.
There are twatches with a moon accruate with a day in 122y but they Don't come anywhere close to the bargain price of the fantastic atmos. In fact you could probably buy an atmos per room for one of these wrist watches.

We cab always all JLC to make a master grande moonphase with a very accurate moonphase. They might just take up the challenge.

THE moon is ALWAYS MOVING, whereas a watch or clock makes a jump each day. Therefore, the watch will show the day of full moon, but not the hour (unless the hour happens at the time that the watch's moon is "full," but then only for that brief interval of time).
The Arnold & Son "True Moon" does keep pretty good track of the moon, but, again, it's not constantly moving.
The best you can do is to set it at the date of the last full moon, then advance the corrector 1 day per phase of moon until you come up to the correct date.
If you want it "easier," the Kurt Klaus perpetual calendar module that JLC uses for the previous "Master Perpetual" or on the IWC Portuguese Perpetual is pre-set at the factory. But the price is a "wee bit" higher than the Master Calendar.

thx for brining this up.
This is a genuine concern ( ) ): what do we actually see when we look at the moonphase of our calendar.

I follow your reasoning. a step is a step and between 2 steps, well, nothing changes. Whic means the display when sync properly displays the real thing only at the time of the next step.

I was under the impression though, that in the case of the Atmos, the moonphase indicator is directly and "constantly" (if it means anything for a clock that receives an impulsion of energy every 30s) driven by the calibre hence the moon indicator is constantly displaying the moonphase by increments of 30s (each beat of the clock). So, if everything is set right at some point, when you look at the moonphase you see it displayed with a 30s accuracy compared to the real phenomenon.
Considering that the moonphase is averaged with a cumulative error of 3s per moon cycle, it will take 10 moon cycles before this cumulative error is bigger than 1 beat. So almost a year with almost perfect moon phase display. (not considering that the clock itself will run a little bit fast or slow over that same period and this would impact the whole system far more, as a couple of seconds per day will turn into a couple of minutes per month... but here you go, this is watchmaking, for mere mortals )

I find it funny that it is quite a challenge to quantify the accuracy of such poetic complication as the moonphase display in various calibres.
I enjoy the logic behind it because I find it incredible to be able to have a mechanical device that represents the position of Earth, Moon and Sun right in front of me.

I think there is also room for new complications displaying or allowing to accurately sync the moonphase on a watch or a clock.
One can hope to be heard by the watchmaking brand we are passionate about.

The Atmos comes the closest, but it would require many, many teeth to represent and accurate, continuous moonphase.
-Dean

You have pointed out correctly the deficiency of the standard moonphase.

What I do is just adjusting it once in a few month. My solution will obviously not satisfy you but what I do is a lot simpler. When I remember, I will just try to adjust to full moon when it is the 15th day of the Chinese calendar month (which is indicated in the home calendar I am using) and normally I don't have to bother about it until I wear the watch again.

Jaw