====== Patek Philippe Perpetual Calendar 5550 ======

{{wst>image_cr|Patek Philippe|Perpetual Calendar 5550}}

[[Patek Philippe]]'s [[2011]] **Perpetual Calendar Ref. 5550** was one of the first wristwatches with a [[silicon]] [[balance wheel]]. It is the fourth member of their [[Patek Philippe Advanced Research|Advanced Research]] project.

===== Overview =====
In the 2000s, Patek Philippe set up an [[Patek Philippe Advanced Research|Advanced Research]] project to address the long-standing issues of [[isochronism]] and durability in watches. The main technology applied to this task was a proprietary alloy of [[silicon]] known as "[[Silinvar]]". The company proceeded steadily, producing first a Silinvar [[escape wheel]], then a [[hairspring]], an [[anchor]], and a [[balance]].

Ref. 5550 was the fourth Advanced Research watch, introduced in [[2011]], and the first with a [[perpetual calendar]]. [[PP 240|Cal. 240 Q Si]] included the Silinvar "Pulsomax" [[escapement]] of its predecessor, this time in the company's fine [[micro-rotor]] automatic movement. It also added a novel Silinvar version of the company's traditional [[Gyromax]] [[balance wheel]] with a 24 karat gold rim and four gold poising screws called **GyromaxSi**. This made it one of the first watches ever produced with a silicon balance and escapement. The [[display caseback]] included a large "[[cyclops]]" magnifier to allow the owner to inspect these high-technology components.

Although it used these high-tech components, Ref. 5550 was nevertheless a Patek Philippe. It included their traditional [[perpetual calendar]] mechanism with day/[[24 hour indicator]] and month/[[leap year indicator]] subdials inset at 9 00 and 3 00, and a date and [[moon phase]] subdial at 6 00. The silver dial features simple applied gold markers at all hours but 6, and a "railroad" seconds track. The hour and minute hands were leaf shaped and featured [[lume]]. It had a traditional Patek Philippe [[platinum]] case, with long integrated lugs.

<WRAP ud ud_mod>
**Reference:**
  * 5550 platinum, 300 produced

**Movement:**
  * [[Automatic]] [[manufacture]] movement [[PP 240|Caliber 240 Q Si]], 28,800 A/h
  * [[Perpetual calendar]] module
  * [[Silinvar]] "Pulsomax" [[escapement]] and Silinvar and gold "GyromaxSi" balance wheel
  * [[Geneva Seal]]

**Case:**
  * [[Platinum]]
  * D 39 mm
  * [[Sapphire crystal]] caseback with magnifying bubble

**Dial:**
  * Silver

**Functions:**
  * Hours, minutes
  * [[Perpetual calendar]] with day, date, month, and [[leap year indicator]]
  * [[24 hour indicator]]
  * [[Moon phase indicator]]

**Limited edition:**
  * 300 pieces
  * Predecessor [[Patek Philippe Annual Calendar 5450]]
  * Successor [[Patek Philippe Aquanaut Travel Time 5650]]
</WRAP>

{{tag>Watch_models Watches_with_perpetual_calendar Patek_Philippe_models Patek_Philippe_references Patek_Philippe_Advanced_Research_models}}