If six turns of a mainspring provides a power reserve of 48 hours and the centre wheel pinion has 10 leaves and a pitch diameter of 3mm, what is the pitch diameter of the barrel and how many teeth will it have?
6 turns provides 48 hours so one turn of the barrel equals 8 hours, which is equivalent to eight turns of the centre wheel. Therefore the barrel has 80 teeth, which means the pitch diameter (working with the same ratio) has a 24mm pitch angle (ratio 8/1)
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