Zenith Caliber 120 pilot watch
A little known complication that can easily go unnoticed in a timepiece, hacking seconds allows a user to stop the seconds hand by pulling out the crown in their watch, enabling them to set the watch more accurately. And although these mechanisms have existed since the 18th century, they’ve never really gotten much attention.
The hacking seconds mechanism really gained popularity in the early 20th century. One would pull out the crown releasing a hacking lever that would interrupt the balance wheel and stop the gear train. As war loomed over Europe, soldiers started to use hacking mechanisms to synchronize their watches and more accurately coordination their movements. In the late 1930s and 1940s, pilots started to use hacking seconds for the same reasons, although coordination was much more critical in the air than on the ground. An example of these watches would be those featuring IWC’S Caliber 89, made by Albert Pellaton himself in 1946 as his first movement after joining IWC. There is also the Zenith Caliber 120, developed specifically for pilots in the 1950s. The mechanism is also useful for celestial navigation, particularly taking sights from different positions on a ship when the marine chronometer is in a fixed position on the bridge. In fact, the early hacking seconds mechanisms were especially important to the development of chronometers and marine chronometers, as the mechanism was used to test the accuracy of the other movements.
Hacking seconds or stop seconds, may be an often overlooked mechanism, but it is significant to the development of watches overall, and more so in specific areas like aviation and navigation. Many brands incorporate the mechanism into their watches today, and greats like Rolex, Omega, and Zenith use it in some vintage pieces, although a few models are extremely rare. You may be surprised to know that Patek Philippe is known for not using the hacking seconds mechanism in most of their watches, as they believe that the sudden stopping can have detrimental effects on the mechanism.