Complication
Moonphase
A little window that follows the lunar cycle.
What it does
A disc printed with moons rotates behind an aperture to mirror the phase of the real moon. A standard moonphase drifts by a day about every 2.7 years; an 'astronomical' moonphase stays accurate for over 100 years.
How to read it
The visible moon in the aperture shows the current phase — new, waxing, full, waning. Set it by advancing to a known full moon.
Impact on value
Positive on dress and complicated watches; largely decorative but adds romance and craft.
Keep reading
ComplicationTachymeter
A bezel scale that converts elapsed time into speed.
ComplicationPower Reserve Indicator
A fuel gauge for the mainspring.
ComplicationPerpetual Calendar
Knows the date, month, and leap years — until 2100.
ComplicationTourbillon
A rotating cage that averages out gravity's error.
ComplicationWorld Time
All 24 time zones readable at once.
ComplicationAnnual Calendar
Knows every month length except February.