I would assume that you should set the date @31 December and then through the crown pass the days until 28th Feb to see whether you reach 29th Feb or 1st March. Once you reach 29th Feb you know that you are on a Leap year.

Jan 19, 2024,07:27 AM
 

Very long and tedious process but I wouldn't see how to do it differently

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Ref 5395 perpetual calendar - how do you set it?

 
 By: xto : January 18th, 2024-03:34
This Blancpain is described by everyone as a. Perpetual calendar but has no leap year indicator. I gather there are some other perpetual calendar watches including the Patek 3448 that also do not have leap year indicators. What I can’t seem to find is any...  

It depends whether you know when it stopped

 
 By: MrkK : January 18th, 2024-16:48
If you know the year when the watch stopped, it is easy to estimate. If you don't, you either send it to manufacturer or risk pressing correctors thousand times to land on the correct year

Ah, the old “only by watchmaker” trick

 
 By: xto : January 18th, 2024-22:21
Still curious as the PC mechanism is usually under the dial so it’d be hard to know what year it’s on from the back. Full dismantling just to set?

Hard to believe

 
 By: watch-er : January 19th, 2024-22:16
they made PCs like this years ago. The early Patek PCs did not have external correctors and had to be set by the factory, I believe.