The patented ZERO-RESET mechanism is a Lange-specific convenience feature. It enables fast and precise timesetting. When the crown is pulled, the movement stops and the seconds hand jumps to zero. This allows the minute hand to be precisely aligned with the respective minute marker, and the watch can be accurately restarted, for instance when an acoustic time signal sounds. This makes it particularly easy to synchronise the watch.
Starting to the second The patented ZERO-RESET mechanism
The mechanism consists of a complex lever system that presses a zero-reset lever against a heart-shaped cam. The seconds hand is attached to the same arbor on which the heart cam rotates. When the heart cam is pivoted into its initial position by the zero-reset lever, this also causes the seconds hand to jump to zero. Pushing the crown home again instantly restarts the movement and with it the seconds hand.
In a modified, even more complex form, this mechanism can also be found in the 1815 TOURBILLON except that here, the tourbillon must be stopped instead of the balance.