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    Calculate Beats and Pendulum Length from Tooth Counts

    If you know the number of wheel teeth, it is easy to calculate the correct pendulum length and the beats per minute.

    Change the items in the yellow boxes and see the Results below.

    Calculator
    BPM and Pendulum Length
    Teeth in Movement:
    Wheel Teeth
    Pinion Leaves
     # of Wheels in Drive Train:
    Escape Wheel:
    5 Wheels
    4th Wheel:
    4 Wheels
    3rd Wheel:
    Center Wheel or Center Pinion:
    Results:
    Beats per Hour:
    Beats per Minute:
    Pendulum Length:
    Tips
    It can be a challenge to count the teeth on a wheel without losing your place. Here are a couple of tips:
    • With a magic marker, place a dot next to the tooth that you will start counting. Now you will know when to stop counting.
    • If the wheel is out of the movement, run the wheel across a sheet of paper and count the holes.
    Formulae:
    BPM = 
    WE x W4 x W3 x WC
    PE x P4 x P3
     x 2 ÷ 60

    or,
    BPM = 
    WE x W3 x WC
    PE x P3
     x 2 ÷ 60

    LP = 
    141120
    BPM2
    where,
    • BPM is beats per minute
    • WE is the number of teeth on the escape wheel
    • W4 is the number of teeth on the fourth wheel
    • W3 is the number of teeth on the third wheel
    • WC is the number of teeth on the center wheel, or center pinion for a 4 wheel train
    • PE is the number of leaves on the escape wheel pinion
    • P4 is the number of leaves on the fourth wheel pinion
    • P3 is the number of leaves on the third wheel pinion
    • LP is the pendulum length

    5 Wheel Drive Train


    4 Wheel Drive Train

    This calculator, provided by Horology - The Index, is one in a series of repair calculations.