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| The heart of the perpetual calendar is another cam with nine steps (the year cam) that makes one revolution per year, containing a smaller cam, (the February cam). Think of it this way, most months have either 30 or 31 days and are stable and don’t change from year to year. OK, nine steps plus one does not equal 12 months, what is going on here? Well, if you think about it December and January, two consecutive months, both have 31 days, then comes February that is the wild card, followed by March with 31 days, April with 30 days, May with 31 days, June with 30 days, July and August with 31 days, September with 30 days, October with 31 days, and finally November with 30 days. It’s the depth of the cam steps that adjust the length of each month, the deeper the step the bigger the adjustment.
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| So what about the wild card month of February? An ingenious little cam, the February cam, is contained within the year cam. In the left photo we can see that the February cam has a small gear attached on the bottom side with 16 teeth. And in the right photo we see a stationary gear with 20 teeth. The year cam rotates on the axle of this gear once per year and given the ratio of 20/16 produces 1 ¼ turns of the February cam each year. Doesn’t seem to make sense does it when you would think that the February cam should make one revolution every 4 years. But if you think about it the February cam still advances ¼ turn every year and repeats its cycle every 4 years, very clever!
So there we have it, an Instantaneous Perpetual Calendar watch from Daniel Roth SA.. This watch is a delight to have on your wrist, just the right size. It could be larger but why? The art of watchmaking is still alive and moving forward…
Best Regards,
Ron DeCorte
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