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How A Chronometer Works Part II |
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Articles -
Watchmasters Corner
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Written by Ziggy Zumba
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Page 2 of 4
The chronograph has 3 selections and modes of
operation:
1 OFF/Reset
2 ON, or Running
3
Stopped
OFF
Here is the cam in the OFF position
ON or Running
To get the chronograph in the ON
position, you press once on the upper pusher (left one in the picture). This moves the cam
this way and the chronograph starts running. Details of what happens on each sub-dial will be
covered in detail. For now we are only interested in the cam.
Stopped
To stop the chronograph, we press the
top pusher a second time, and this is the position of the cam, it is not the same as the OFF
position.
Only in the Stopped position is the bottom pusher functional.
See here how the arm can now press on this tab on the cam.
When it’s running, the bottom pusher misses the arm, see
here:
Reset
From the stopped position,
pressing the bottom pusher will cause the cam to move as follows and return the cam to the OFF
or reset position.
When starting the chronograph you will feel a fair amount of
resistance, and after you see all the levers and springs that are being moved around, you will
know why. Going from the running to the stopped setting, doesn’t take much force on the
pusher. Resetting the chronograph to the OFF position, again takes some force. All this is
normal.
Now that you know how the cam works, lets build a chronograph one sub-dial at a
time.
Running seconds
Running seconds.
The 2nd wheel is the one
that turns once every minute. It is part of the basic movement and has an extended post on the
dial side. This post sticks up at the 9 o’clock position on the dial, and is where we attach
our hand for running seconds. Running seconds means that this indicator always shows sweeping
seconds as long as the watch is working.
That’s it for the running seconds (I wish they were all this
easy….).
12-Hour sub-dial
Next on our list is the 12-hour sub-dial. In
part 1, I went into detail on the mainspring barrel and the extra gear on the top of it and
where it was located on the dial side of the movement. Here it is. Do you remember
it?
The mainspring is the heart of the whole watch, if
it is not turning, then nothing else is. As long as the watch is running, this gear is
turning.
The 12-hour sub-dial is driven by this gear assembly:
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Last Updated ( Tuesday, 14 August 2007 )
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