A perpetual calendar is like a small computer on your wrist.

Think of it this way: Imagine a watch that keeps track of not only the time, but also the date, the day of the week, and the month, and also tells you whether it’s a leap year or not, and what the current phase of the moon is. Oh, and one more thing — imagine it does all of this mechanically, using springs and gears, and that you only have to adjust it once every century or so. Crazy, right?

Patek Philippe likes to take this one step farther, however: In the early 1940s it released the model 1518, the first serially produced perpetual calendar chronograph, which combined the aforementioned qualities of the typical quantieme perpetuel with those of the chronograph for recording elapsed time. Since then, the firm has further cemented its place as the foremost watchmaker in the world with more QP chronograph models. 

The particular perpetual calendar chronograph we have here is the reference 5270G-001. Housed in a 41mm, 18K white gold case, it features a signed crown, polished concave bezel, sapphire crystal, and sapphire display back — a thoroughly modern watch despite its square pushers, horn lugs and classically inspired layout. The dial is striking, executed in a satin silver finish with radial subregisters, applied indices, a matching feuille handset, and an English calendar. Powered by the manually wound Patek Philippe Cal. CH 29-535 PS Q movement, it’s fitted to a signed, black alligator leather strap with matching, signed white gold deployant clasp. 

It would be enough to enjoy this innovative wristwatch on its own, but this particular timepiece also comes with its inner and outer boxes, books, leather folder, solid white gold caseback, signed calendar corrector, serialized hangtag, and certificate of origin from Patek Philippe confirming its sale in 2013.

Any old wristwatch can tell the time. Few truly define it.