Complications · Aug 21, 2026 · 4 min read
Why a moonphase drifts, and why ours barely does
A standard moonphase is out by a day every two and a half years. Ours needs correcting once every 122.
A lunar month lasts 29 days, 12 hours and 44 minutes. Most moonphase discs have 59 teeth and assume 29.5 days, so they slowly fall behind the real moon.
The Meridian Moonphase uses a 135-tooth disc and an extra reduction wheel. The result drifts by a single day in 122 years.
