“Grosse Pièce” is a historically important yellow gold double-dial and double open-faced, minute repeating astronomical watch with one minute tourbillon, a celestial chart for the night time sky of London, day/night grande and petite sonnerie, chronograph, register for 60 minutes and 12 hours, perpetual calendar, moon phases, equation of time, power reserve, and 24-hour sidereal time.
Made for S. Smith & Son Ltd., work on it started in 1914 and the creation shown at the Geneva Watch Exhibition in 1920 before being delivered in 1921.
Movement: No.16869, with English-style, three-quarter plate, “Swiss” lever escapement, and one-minute tourbillon with three-arm polished steel cage.
Dial 1
Front: white enamel mean time dial, Roman numerals, four subsidiary dials indicating perpetual calendar calibrated for leap cycle, date combined with day of week, register for elapsed 60 minutes and 12 hours, ages and phases of the moon combined with up/down indication, the outer ring calibrated for equation of time.
Dial 2
Back: Sidereal time, the dial silvered and gold over engine-turning, calibrated for 24 hours, in Arabic numerals enclosing an aperture revealing the celestial chart and its progress over London (51.5072° N, 0.1276° W) at any time of the day or night.
The chart shows 315 stars and various labelled constellations, all labelled in gold against a blue enamel ground. Two silvered plaques over the celestial chart state the labels Western Horizon and Eastern Horizon.
Olivette hand setting for each dial.
