Why was the 12-hour counter on a chronograph invented? / Mainspring Q&A - Answering your watch questions

Q: Why was the 12-hour counter on the chronograph invented?

A: Because it became possible for aircraft to fly long distances.

12-hour counters are now commonly found in mechanical chronographs. While they allow for longer measurement times, they also make the mechanism more complex and more expensive. This mechanism is said to have originated in the mid-1930s, when manufacturers such as Martell (now Zenith) and Valjoux (now ETA) successfully incorporated 12-hour counters into their mechanical chronographs.

What these watches have in common is that the 12-hour counter is powered directly from the barrel rather than being powered by the chronograph, which is why most 12-hour counters are now located at 6 o'clock on the dial.

So why did the 12-hour counter come into being in the 30s? One reason is said to be advances in aircraft. Many new aircraft capable of long-distance flight were developed during this period, and the previous 30- or 45-minute counters were no longer able to measure flight time.

On the other hand, chronographs without a 12-hour counter are intended for professionals.

Of course, chronographs without a 12-hour counter were also produced in the future. These were intended for professionals who needed to measure short periods of time. The so-called Doctor's Chrono is one example.