First launched in 1936, the Longines 13ZN chronograph movement is still considered today as one of the most beautiful and technically interesting wristwatch chronograph movements ever produced. The 13ZN was designed as a flyback chronograph, where a user can quickly reset the chronograph seconds hand to zero while it’s still running. Longines initially intended for these wristwatches to be used as tools for military personnel and aviators. Watches fitted with the caliber 13ZN were housed in cases ranging in size from 34mm to 38mm, and were produced with either snapback or screw-down casebacks.