The Chronomètre FB 1L.4 by Ferdinand Berthoud is a marvel of intricate mechanics and craftsmanship. The watch combines a tourbillon movement with a unique moon-age indicator, giving the wearer a precise reading of the moon’s age and phase. Additionally, the watch features a dial opening between 4 and 5 o’clock that shows the current moon phase, waxing or waning, thereby indicating whether the moon-age indicator hand is rising (up to day 14) or returning (to the new moon). This complication, combined with the constant force of the FB-T.FC.L calibre, ensures astronomical precision corresponding to a one-day difference in 577 years of operation. This timepiece was produced in a ten-piece limited edition.