How to Adjust the Pendulum on a Seth Thomas Clock

By Mark Slingo ; Updated October 06, 2017

A pendulum regulates the speed at which a pendulum clock runs. The speed at which a pendulum swings is dependent on the position of a weight in the pendulum and the length of a pendulum shaft. Seth Thomas was an American clockmaker who produced tall, mantle and other types of clocks. You can adjust the pendulum to regulate the speed in a Seth Thomas clock either on the face or using an adjustment knob on the base of the pendulum.

Things Needed

  • Watch
  • Square key

On the Dial

Note the time on the clock. Adjust the clock's time to match the time on your watch.

Check the clock time at the same time on your watch one day later. Decide whether the clock is running fast or slow.

Insert a square key into the slot below the center of the dial on the clock face. Turn the key clockwise to slow down the clock; counterclockwise to increase its speed.

Continue to check and adjust the clock for six days.

On the Pendulum

Note the time on the clock. Adjust the clock's time to match the time on your watch.

Check the clock time at the same time on your watch one day later. Decide whether the clock is running fast or slow.

Turn the adjustment nut on the base of the pendulum clockwise to speed up the clock; counterclockwise to slow it down. One complete turn will alter the time in 24 hours by one minute.

Check the clock every day at the same time for six days to see if the clock requires more adjusting.

About the Author

Mark Slingo has been a professional writer since 2008. His work has appeared in Forward, ScubaGlobe, Scuba Jedi, "Pattaya Mail" and other publications. Slingo has a Bachelor of Arts in politics from the University of Newcastle and a diploma in journalism from the British College of Journalism.