Editorial
The Master Ultra Thin Moon 39mm puts a genuinely thin automatic movement , 3.9mm, caliber 925/1 , under a moon phase display accurate to one day's drift per 1,000 years. That combination of mechanical thinness and astronomical precision is nearly impossible to find below $15,000. This is JLC doing what it actually does well: useful complications built with real craft, not marketing filler.
Jaeger-LeCoultre introduced this reference in 2016 in steel (Q1368470) and rose gold variants, with Q1368420 designating the steel case in silver dial configuration. The caliber 925/1 traces its architecture to the long-running 920 family, refined to 3.9mm total movement height. The 39mm diameter kept the proportions close to vintage JLC dresswatch tradition rather than chasing the 40mm+ trend of the era.
Production continues as of 2025 with minimal spec changes, which speaks to how settled the design is. Limited dial variations exist , sector dials and blue sunburst dials have appeared but the silver/steel combination in Q1368420 is the most traded reference.
The crystal sits very close to the dial on an ultra-thin case, so even minor bezel strikes can crack the sapphire without obvious external damage to the case. Check the moon phase disk carefully: the hand-painted or lacquered disk can show wear at the star cutouts if the watch was dropped or serviced carelessly. Case polishing is a real concern on these thin bezels , over-polished examples lose the crisp anglage and look anonymous.
Confirm the crown is seating fully; the 30m water resistance rating on 925/1 is marginal and a worn crown seal will push it below that quickly. Ask for service history: JLC movements in this price tier are sometimes left unserviced longer than they should be because owners assume dress watches run dry forever.
