The first push releases both hands. While one continues registering the time, the other hand can be repeatedly stopped. In order to stop and bring both hands to zero a watch has a return pusher. The position of the pusher, controlling the split-seconds function is usually at either 10 or 8 o'clock.
In 1922 Patek Philippe launched into the market its first double chronograph. Today Double chronographs (or Rattrapante Chronographs) can be divided into two subgroups. One comprises chronographs based on in-house movements of different watchmaking companies and the other group contains timepieces based on movements like the Valjoux 7750 from ETA.
The group of the in-house movements began with the Venus series of calibers: 179, 185, 189 and 190. These calibers had a rattrapante pusher on the crown but since 1952 they are no longer in production.
The first split-seconds mechanism based on the ETA-Valjoux 7750 was presented in 1992 at Baselworld. Today this caliber is the main one used in watches with a split-seconds mechanism.