Longines Stopsecond 5681

Longines. A rare and unusual stainless steel single button fly back chronograph wristwatch with black dial and central minute register Signed Longines, Brevet, Stopsecond model, ref. 5681 movement no. 7'402'750, case nos. 23'646 and 8, manufactured in 1950 Cal. 12.68 Z mechanical movement, 17 jewels, black dial, luminous Arabic numerals, luminous hands, outer Arabic five minute railway divisions for 60 minutes register with central minute hand and central chronograph seconds hand, outer tachymetre scale, engine-turned subsidiary seconds, circular case, stepped bezel, snap on back, fly-back chronograph mechanism operated through a circular button in the band, case, dial and movement signed 37 mm. diam.