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When a long central second hand – and chronographs usually time seconds with a long, easy-to-read central second hand – gets reset back to zero, it’s like a crash test car hitting the wall. It’s a brutal stop from a relatively high speed. The long hand reverberates back and forth as it swings to a stop, causing stress and wear of the components. It’s not the instant reset that the eye sees as this video below illustrates.

The dial side regulator of the Grönograaf dampens excessive speed of the chronograph’s fast, flying resetting central hand as well as the smaller 30-minute hand, virtually eliminating the shock and wear undergone by all other chronograph movements when resetting (Agenhor AgenGraphe movements excepted).

Grönefeld 1941 Grönograaf

Tour of the Grönefeld Grönograaf’s dial

A counterclockwise tour of the Grönograaf’s dial reveals an hour-and-minute subdial at 1 o’clock for reading the time, an arc with a blue arrowhead indicating the state of the 53-hour power reserve, a running seconds subdial at 9 o’clock, the chronograph’s 30-minute counter at 6 o’clock, and that eye-catchingly blued chronograph central second hand.

Grönefeld 1941 Grönograaf regulator

But the first thing that attracts attention on the dial is at 3 o’clock: that silent centrifugal regulator with its two shiny gold weights. That regulator spins when the chronograph is reset, and when resetting the central second hand and, to a lesser extent, the 30-minute hand move too fast, energy is transferred into spinning those gold weights so the chronograph hands reset at an optimal speed.

Centrifugal regulator

To my knowledge, all chronograph mechanisms reset the seconds and minutes by using hammers hitting heart-shaped cams. Pushing the reset button causes two steel hammers to forcefully hit and rotate the two cams. Those cams pivot at the axis of the chronograph’s minute and second hands. It’s the violent micro shock of these hammers hitting the cams that is transmitted into the resetting hands and reverberates in and around the movement that causes wear and can disrupt the timing.

And it’s the long central second hand that cops the worst of the shock: it oscillates frantically after its base hits a brick wall at high speed. And in other unfortunate news, the hand is usually friction-fit on its post and can be loosened by the micro shocks. That’s why central chronograph second hands are usually made as thin as possible (for low mass) while still being legible. A lighter and easier-to-move central second hand also means less load and wear on the movement when the chronograph is running.

Grönefeld 1941 Grönograaf

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