The AP reference 5516 was the world’s first perpetual calendar wristwatch with leap year indication, of which only nine were produced, succeeded by the later reference 5548, with caliber 2120, introduced 1978.

The caliber 2120 is one of the most recognized movements in horology known for its long history and jointly developed by Audemars Piguet, Jaeger-LeCoultre, Vacheron Constantin, and Patek Philippe. The movement for decades was the thinnest automatic movement with central rotor, and distinguished by the 21K gold rimmed rotor. Based on the success of the reference 5548, Audemars Piguet released the reference 25558, their first skeletonized perpetual calendar wristwatch. Research indicates 217 examples were made with 154 in yellow gold like the present example.

These fully skeletonized watches allowed for a breath taking view of the movement from both the front and back. They exemplified the very best of Swiss watchmaking, where non-essential metal from all of the movement’s plates and bridges were removed, and all remaining “skeletal” parts were hand engraved and finished.

The present yellow gold timepiece is incredibly striking displaying the month, day, date and moonphase through the sapphire crystal dial. The black numerals and blue moon phase sector contrast nicely against the yellow gold case. The watch is in excellent overall condition and was recently serviced by Audemars Piguet. At 36 millimeters, the case size is perfect for any occasion, making the reference 25558 a wonderful watch for the connoisseur.