The 13ZN is the chronograph calibre that Longines developed and patented in 1936, and the watches that carried it. It is a manually wound 17-jewel movement whose defining function is the flyback, which lets the wearer reset the running chronograph seconds hand to zero and restart it with a single push. Watches fitted with the 13ZN were made in cases from 34 to 38 mm, and occasionally larger, with snap or screw-down casebacks. A 1943 reference 5009 sold by Phillips shows a typical example: a 38 mm stainless steel case with a slim profile, a two-tone silvered dial with tachymeter scale and the 13ZN flyback calibre. It matters as one of the most important wristwatch chronograph movements of its era.

Longines initially intended these chronographs as tools for military personnel and aviators. The 13ZN was the most elaborate chronograph of the brand at the time and was offered in several versions, with 30- or 60-minute counters and one or two pushers; some early single-pusher examples lacked the flyback. Well-known references include the 4974 “Tre Tacche” and the 5699 “Doppia Lancetta”, which uses two central chronograph hands to record both seconds and minutes. Watches for the American market were imported through Longines-Wittnauer and carry the LXW stamp on the movement. The calibre remained in use into the late 1940s before being succeeded by the 30CH.

Collectors and auction specialists regard the 13ZN as one of the most beautiful and technically interesting wristwatch chronograph movements ever made, in the words of Phillips, and it is a favourite of vintage chronograph collectors. Results reflect this: the 1943 reference 5009 sold at Phillips for CHF 23,750 against an estimate of CHF 12,000 to 18,000, a 1947 reference 5699 “Doppia Lancetta” reached CHF 62,500, and a 1942 reference 4974 “Tre Tacche” sold for $60,000. As with other vintage chronographs, originality of dial and case is the main concern for buyers. The 13ZN is no longer produced; it is found today only in vintage Longines chronographs.