1940s Longines Stop Second Turning Bezel Rare Round Pusher

Longines, stop second, turning bezel, rare round pusher, circa 1940s. 
Stop-seconds with a turning bezel usually have a square pusher, but the round pusher is a super rare piece from a time when Longines was experimenting with waterproof models, including the 13zn. The addition of the water resistance function not only improves the practicality of the watch, but also increases the power of the design by adding round pushers to the massive case of the turning bezel. The rarity of this model is further enhanced by its excellent state of preservation.