In this case study we are looking at the split seconds mechanism and how it works.
A chronograph, once operated, tracks the elapsed time – and, between 58 seconds and +1 seconds, will engage the minute register and continuously move it until it flicks over to indicate one minute duration. These counters can be 30 or 45 minutes.
A split seconds allows you to have a second Chrono runner which can be stopped independently – and, once depressed, instantly catches up with the Chrono runner. It could have been invented, for example, when a runner finishes a race. You can stop the split and find out how many seconds behind you were. This is useful information if you need to work on how many seconds you need to improve on. In this example of a pocket watch made around 1880, the split mechanism sits under the watch dial.
Here is a heart-shaped cam – and in this image, you can also see the split pillar wheel and mechanism. The pillar, once depressed, allows the arms to be opened and closed. You will notice a tiny heart-shaped cam in the middle of the movement and this is fitted by friction to the Chrono runner. This can be positioned in any place on the wheel arbor.
This wheel sits on top of the heart-shaped cam; the spring pushes the lever with the tiny semi-circle jewel and rests against the flat of heart-shaped cam when running together. When the pillar wheel is depressed, the arms close – and, this time, the split wheel will ride around the shape of the heart-shaped cam.
The split is stopped and started by these arms. Both levers and split wheel have fine but unusable meshing teeth that, when stopped, give enough friction to stop the split wheel instantly and prevent any creeping of the split wheel (thus giving a false reading).
In this image, the arms are open and the semi-circle jewel will follow the heart-shaped cam flat and follow the runner.
This image shows hands in place. As the arms are open, the split hands sit underneath the Chrono runner and, in sequence, record the same time together.
This time, the chronograph has run and the split has stopped. The Chrono runner has continued and there is separation. The split hand will not move until depressed, to join the Chrono runner regardless of how many minutes or seconds have passed.
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