A moonphase display adds a view of the lunar cycle to a watch. It can be an enjoyable detail in a daily rotation, provided you understand what it shows and how to keep it aligned. Begin by identifying the function: a moon pictured on a dial does not always indicate the phase of the Moon.
Read it over a lunar month
The cycle from one new moon to the next lasts approximately 29.5 days. IWC’s moonphase explanation describes how gearing approximates that cycle. It is different from both a 24-hour day and the changing lengths of calendar months.
In a conventional aperture, a complete moon disc centred in the opening represents full moon. As the display advances, the visible portion changes. Consult the watch’s diagram to distinguish the approaching and receding phases rather than guessing from the side on which a crescent appears. Display designs differ.
Separate moonphase from a day-and-night display
The IWC Portofino Day & Night IW459806 uses a disc that completes a rotation every 24 hours, showing sun or moon according to the time of day. That is a day-and-night indicator, even though its artwork includes a moon.
Read the specification and manual before assigning a function to an attractive window. Ask whether it follows the lunar cycle or the daily passage of time. Neither display is inherently better; the distinction tells you what information you can expect to read and what may need adjustment.
Use the setting method for the actual calibre
The Longines L296 manual describes a method that begins with a centred full moon, then advances the display according to the days since the last full moon. This illustrates a reference-based setting method, not a universal sequence of crown turns for every moonphase watch.
For your watch, confirm the correct reference date, control, direction and any restricted adjustment periods. Follow the instructions for moonphase and calendar functions separately rather than assuming their precautions are identical. If the procedure is unclear, ask the maker or a watchmaker before experimenting with the controls.
Check the display when returning to the watch
After time out of rotation, check the ordinary time, calendar and moonphase independently. A correct date does not prove the moonphase is aligned. Our date-display guide considers the separate calendar-setting task; use the moonphase instructions for the lunar display.
Then view the whole dial at normal wrist distance. Can you read the time comfortably while enjoying the extra detail? Use our dial-legibility checklist in ordinary light, and choose a display whose appearance and upkeep suit your routine. Explore Watches & Wear for related guides.