What could be more poetic than watching the cycle of the moon on the dial of a watch with moon phases? New moon, first-quarter, full moon, last quarter: the cycle is as unchanging as the spectacle is majestic. The precise duration of a lunar month is 29 days, 12 hours, 44 minutes and 2.8 seconds, or 29.53 days, which is displayed on most models as 29.5 days. The difference between a watch mechanism with moon phases and the true length of a moon cycle thus results in a one-day deviation every 2 years, 7 months and 20 days. For watches with more sophisticated moon phases, the precision of the lunar month is 29 days, 12 hours and 45 minutes, creating a one-day deviation only once every 122 years. The moon phase indicator generally completes the perpetual calendar. This is the case of the Jaeger-LeCoultre Master Grande Tradition Quantième Perpétuel 8 Jours SQ, Calibre 876SQ. It can also feature alone, as on the Rendez-Vous Moon, Calibre 935, where the lunar months appear surrounded by the night sky.