How to Determine the Proper Pendulum Length for a Clock

Before electricity, stand-up clocks were powered by weights that moved the hands and were regulated by swinging pendulums that controlled their speed. How fast the hands move depends on how long the pendulum is (the shorter, the faster). Adjusting a grandfather-clock pendulum to the right length is, like most things having to do with grandfather clocks, something that requires a lot of patience and attention to detail.

Things You'll Need

• Independent source of the correct time

Instructions

1. Manually set the clock to the correct time, as based on an electric watch or clock or searching for the time online. Set the clock by opening the face and moving the minute hand counterclockwise to the correct time. Do not move the hour hand (it will move in conjunction with the minute hand).

2. Check the clock 24 hours later against the same timepiece you measured it at the first time. If the clock is more than a minute off, the pendulum needs to be adjusted.

3. Locate the "pendulum bob,'' a metal nut at the bottom of the pendulum. If the clock is running too fast, turn the nut to your left, to lower the pendulum and make it run slower. If the clock is running too slow, turn the nut to the right, the raise the pendulum and make it run faster. Make one full turn of the nut for each minute that the clock is off.

4. Reset the time again to be correct. Repeat the checking and adjusting process the following day, continuing daily until the pendulum is adjusted to the right height.

References

• Wayne Berry, Certified Clockmaker: Grandfather Clock Repair