Flyback chronograph

On a traditional chronograph, any new time measurement must be preceded by first stopping and then zero-resetting the hands. Some situations nonetheless call for being able to restart a measurement without any loss of time or concentration. Such is notably the case in airborne navigation, which uses speed, course-change angles and flight times to determine a plane’s position.

While the flyback chronograph is equipped with the traditional two ‘start/stop’ and ‘zero-reset’ pushers, it is possible to activate the ‘zero-reset’ function while the chronograph is in use, meaning no transition via the ‘stop’ phase. This operation instantly brings the hands back to point 0, before starting a new measurement as soon as the pusher is released. The operation can be repeated as often as necessary.

In mechanical terms, the hammers striking the zero-reset heart cams simultaneously disconnect the chronograph wheel from its driving function – or indeed any other function.

On July 25^th 1909, Louis Blériot became the first man to fly across the Channel, covering the 38km distance in 37 minutes. On May 20^th1927, Charles Lindbergh put his name in the history books by flying from New York to Paris across the North Atlantic in 33 hours and 30 minutes. The conquest of the skies was under way. But the larger the distances being covered, the more visual flight mode revealed its limitations.

Aviation would thus take cues from sailing in developing piloting techniques. The ground speed, course, wind drift and flight time thus became essential data in calculating position and called for a distinctive kind of chronograph.

In 1936, Longines became the first company to patent the flyback function on a wristwatch. Like many watch industry developments, its military use would ensure the success of the flyback chronograph. In the early 1950s, the French Ministry of Defense drafted an extremely stringent set of technical specifications regarding the production of watches intended for pilots. Better known as Type 20, this document provided details of the must-have features of such instruments, including a black dial, luminescent Arabic numerals an oversized crown and the flyback function. These specifications were slightly altered in 1956 and renamed Type 21.

A number of manufacturers responded to various military bids for tender. Among them were Breguet, Dodane and Auricoste. Civilian versions, known as Type 20 and Type 21 chronographs, were subsequently commercialized.

More recently, brands such as Blancpain have equipped diver’s watches with the flyback function. Operational even under water, the chronograph can thus be used to calculate decompression stops.