The alarm on these clocks is a simple affair and easy to retro fit which is a bonus as many over the years have had parts go astray often leaving clocks with just a few parts of the system that no longer work.
Be aware if looking for parts of the height of your clock as the two most common case sizes are 25.5 cm and 31.5 cm.
The alarm works by turning a round brass disc that sits behind the hour hand. Typically the hour hand is of a pattern that has a hole that allows you to view through and line it up with and engraved number (1 to 12) set as a clock face on the disc. When you choose your number and line it up behind the hour hand this is your alarm time. Be aware though that like the hands of a Comtoise clock you must only turn this disc clockwise, to do other can result in damage. It only works if turned clockwise.
More accurate alarm setting is down to guesswork between the hours. Even set at your preferred time the alarm may well go off any time 15 to 20 minutes either side! These are old clocks and tolerances are not at modern levels. I suspect also that in the early 19th century an alarm roughly at 10 to remind you of a visit was good enough.
Another aspect to the accuracy is that once set these alarms rely on friction between the disc and hour hand and should the two slip a little between when set and when activated accuracy further suffers.
This friction then holds the disc in place behind the hour hand, the two then travel round the dial together until the hour hand reaches the set time and the alarm goes off.
However, do not be disheartened with a little patience and observation of when your own clock 'goes off' and very minor adjustments you can, (at least i have!) manage to get the accuracy into a ten minute window.
The photo shows the alarm disc set for 11 oclock.
More to follow......
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