The metronome is one of the rarest Patek Philippe mechanisms. To date, only five of these mysterious timers are known, all identical and numbered with a single digit serial number:
1. In Geneva's prestigious Patek Philippe Museum, exhibited at "Exposition de la fabuleuse collection privée de Patek Philippe" in 1989 (Exhibit no. 498)
2. No. 2, the present example
3. No. 4, in private collection
4. No. 5, formerly in the Time Museum (Inv. 2616), sold at public auction in 2002
5. Sold at public auction in Geneva in 1980
All feature the same musical score on the dial, believed to be a folk song based on a 16th or 17th century tune. One can only assume that these chronographs were made to commemorate an event at which the song was performed, possibly an event organized by Patek Philippe. There are other watch series by Patek Philippe known to exist with a different numbering system, including some of the most extraordinary pieces destined for expositions which were not entered within the usual register. One of these timepieces, a magnificent carriage clock, most likely destined for the 1851 London Exposition, is now in the Patek Philippe Museum.