[Aquaman]

Originally Posted by Russell996

Moon phases are always an interesting topic. The correct period (synodic month) is 29 days, 12 hours, 44 minutes, 2.9 seconds. The actual time to rotate the earth (sidereal month) is 27 days, 7 hours, 43 minutes and 11.5 seconds but due to the earth and moon moving around the sun the angle of illumination has changed and hence the apparent phase is longer.
1 day in 122 years is actually a very low level of accuracy and equates to about 12 minutes a year and as you have spotted the setting is not very accurate but probably adequate given it's overall accuracy (I assume for best accuracy you can set the piece to full moon date, set the time to GMT full moon time and set the full moon on the display - then adjust the time back/forward multiple days as required to get the watch date and time set correctly?).
Pieces like the UN Tellurium run with an accuracy of 1 day per 144,000 years (0.6 seconds per year) and are always set to a full or a new moon as the starter point before setting the time - it also shows the actual position of the moon around the earth and the earth/moon in relation to the sun. (plus many other things including world time, perpetual calendar, solar and lunar eclipses, sunrise and sunset times for all points on the earth etc etc)

Images from UN Trilogy of Time Book.

Head fecked