The 855P is a self-winding mechanical movement with a perpetual calendar and is one of the thinnest ever made: only 5. 6 mm. It is a genuine mechanical time program that automatically masters the irregularities of the calendar such as leap years and months of 30 or 31 days, up to the year 2100. The perpetual calendar is still one of the major complications of Fine Watchmaking. This movement indicates hours, minutes, small seconds at 4 o'clock, months and leap years at 12 o'clock, the day of the week at 9 o'clock, and the date at 3 o'clock. The 855P movement sets itself apart from most other perpetual calendars by displaying a second time zone with two hands on a counter at 8 o'clock which can be easily altered without affecting the calendar. The day of the week and the date are both retrograde displays.
Circular Côtes de Genève, a circular-grained mainplate, bevelled bridges, blued screws and a black oscillating weight engraved with the Piaget coat-of-arms add the finishing touches to this movement and are reminders of the Swiss watchmaking brand's high aesthetic values.