Jaeger LeCoultre, Master, Model: 1558420, Automatic mechanical, stainless steel, case diameter: 39mm movement: Jaeger-lecoultre's self-produced 866 / 1 automatic movement has a thickness of 5.65 millimeters, a frequency of 28,800 vibrations per hour, and is equipped with 32 jewels and 305 components, with a power reserve of approximately 40 hours • Case: Made of stainless steel, 39mm in diameter, 10.6mm in thickness, and water-resistant to 50 meters • Dial: Silver sunray-patterned dial, with rhodium-plated conical hour markers and toffe-shaped hands; At 12 o 'clock, a dual calendar window for the day and month is set, and at 6 o 'clock, a moon phase display panel (with a small seconds function) is set. The end of the central hand has a red crescent-shaped date indicator, allowing direct reading of the 31-day date scale on the outside • Crystal: An artificial sapphire crystal, paired with a transparent case back made of the same material, allows for a direct view of the movement's finishing details