Extremely rare and beautiful Longines Ref 13ZN Flyback Chronograph with oversized 37.5mm stainless steel case, and with both stepped curved lugs and stepped case. The case was made with fixed lugs, which points to the origin of this timepiece as a military or aviation tool. The dial is the super-rare 36mm variant that is the largest dial Longines made for the 13ZN chronograph. The size of the dial makes this watch read larger on the wrist, my guess was 40mm when I measured it. Of course the largest 13ZN was 38mm, so if you see one at 40mm, run for your life. The dial has the original lume in excellent condition on the arabic numbers and hands. The ref 13ZN chronograph movement was launched in 1936 and was at the time the leading edge of chronograph production, introducing the world’s first flyback function in a production watch. The flyback feature allows the wearer to reset the chronograph without having to stop it first. This added feature increased the case size of the early ZNs, making them quite big for the era (a time when men’s watches ran 30-33mm) and set the tone for pilot’s watches tending toward larger case sizes. To this day, 13ZN continues to captivate collectors and watch scholars. Archival Papers from Longines confirm serial numbers and sale in Bratislava, 1946.