This is Patek Philippe's current micro-rotor automatic movement.
Calibre 240 is a venerable but respected watch movement, dating back to 1977. It uses a micro rotor for automatic winding to keep the movement as thin as possible, and thus serves as a platform for many complications in Patek Philippe's range of thin watches. To this end, most Cal. 240 movement variations omit a seconds hand. The thinnest Cal. 240 movements are just 2.53 mm thick (2.4 mm as measured by some), while even most more-complicated models are under 4 mm. The largest and thickest model in the family, Cal. 240 LU CL C, uses a special 38 mm plate and is 6.81 mm thick, quite an anomaly in this family.
Like most movements from the 1970's, Cal. 240 beats at a leisurely 21,600 A/h. This contributes to its respectable power reserve, up to 48 hours, but requires careful tuning to maintain accuracy. This is accomplished with Patek's well-known and respected two-spoke Gyromax balance which has eight internal weights for adjustment.
Calibre 240 has the distinction of de-throning one of the longest-running and most-loved watch movements of the century, Patek Philippe's Cal. 27-460. This full-rotor automatic movement lasted in production from 1960 until 1985, when the thin aspect and proven mechanics of Cal. 240 finally pushed it to retirement. The fact that Cal. 240 remains actively in use today in many of Patek Philippe's watches is telling: Between this movement and Cal. 27-460 (itself closely related to the original automatic movement, Cal. 12-600 AT), these two movement designs have powered Patek Philippe's high-end automatic watches for over 60 years!
In 2000, Patek Philippe launched an Advanced Research project to develop next-generation watch components. One major area of development was silicon escapements and balance wheels, both of which were used in a special variant of this movement, Cal. 240 Q Si. As implied, this reference includes a perpetual calendar, moon phase, and 24 hour display as on the 240 Q, but adds some novel high-tech components:
- The GyromaxSi balance wheel is an hourglass-shaped balance composed of silicon and gold weights, replacing the traditional wheel
- The escapement wheel and anchor are constructed of silicon
- The Spriomax hairspring is also constructed of silicon
Patek pairs Cal. 240 with various complication modules:
- Cal. 240 - No seconds hand (27.5x2.53 mm, 27 jewels)
- Cal. 240/152 - moon phase indicator, power reserve, sub-seconds
- Cal. 240 SQU - No seconds hand, skeletonized (27.5x2.53 mm, 27 jewels)
- Cal. 240 HU - 24 hour day/night indicator for all timezones (27.5x3.88 mm, 33 jewels)
- Cal. 240 LU CL C - Date, moon phase, celestial display, date by central pointer (38x6.81 mm, 45 jewels)
- Cal. 240 PS C - Date, small seconds (30x3.43 mm, 27 jewels)
- Cal. 240 PS IRM C LU - Date, small seconds, moon phase, power reserve indicator (31x3.98 mm, 29 jewels)
- Cal. 240 Q - Perpetual calendar, moon phase, 24 hour display (27.5x3.88 mm, 27 jewels)
- Cal. 240 Q Si - Perpetual calendar, moon phase, 24 hour display, "Oscillomax" silicon components (27.5x3.88 mm, 27 jewels)
- PP 324, the current central-rotor automatic movement