As many know, vintage Longines is synonymous with in-house chronograph movements. These calibers were not only pretty but designed with exceptional functions such as an instantaneous minute counter (13.33Z) and fly-back capability (13ZN and 30CH). A lesser known complication that the firm offered was a pointer-date. Though not nearly as technically impressive, these uncommon watches present a neat opportunity to see how Longines executed such a complication in the 1940s. Below is a description of how I believe the mechanism works. Friction-fit on top of the hour wheel (1) is a pinion (2) that drives another wheel (3), with a slot near its center. This slotted wheel makes one full rotation every 24 hours. As the slotted wheel rotates, a cam (4) beneath the wheel is dragged along by a pin that protrudes through the slot. Some minutes before 12 o’clock, the pin of the cam comes in contact with the date wheel (5). The date wheel has 31 teeth, one for each day of the month. When fully assembled, the pointer-hand attaches to the date wheel. Driven by the pin, the date wheel gradually rotates until the cam spring (6) comes in contact with the leading vertex of the cam. At this point, the cam rapidly rotates until the spring meets the flat side of the cam. This rapid rotation advances the date wheel by one day. Note the increasing radius and particular shape of the slot in the 24 hour wheel. Also note that the cam is free to move eccentrically. These design elements ensure that the rapid rotation of the cam is along the proper path to effectively advance the date wheel. A big thank you to watchmaker @Mitka for posting these photos on his website: https://mitka.co.uk/
Thank you for sharing this very interesting info @DirtyDozen12 I`m still hoping to find one of theese beauties out in the wild
@Radiumpassion My pleasure! A few well-known dealers have them but they do not often appear elsewhere. Good luck on your hunt.
Somebody presented one at a Spanish forum several weeks ago and my first reaction was thinking that it was a fake, because I had never seen one before. They are indeed difficult to see in the wild.