Temperature has an effect on all pendulums in varying degrees based on their weight and material. Metals used in the manufacturing of many clock pendulums are susceptible to expansion and contraction during warm and cold weather. Wooden pendulums used in cuckoo clocks also react to temperature fluctuations, although not nearly as much as those made of metal. A suspended pendulum is lengthened when warm, causing the clock to slow down. When cooled, the pendulum contracts, and the clock speeds up. Adjusting for these periodic differences is key to accurate timekeeping.
Stop the pendulum if it is in motion. Pull the weights to their fully raised position.
Set the time on the cuckoo clock by rotating the minute hand slowly clockwise. Adjust the time exactly with that of a digital timepiece. Either a clock or watch works fine for time comparisons.
Set the pendulum in motion and allow the clock to operate for 24 hours.
Check the time on the cuckoo clock and compare its accuracy with the digital timepiece. Stop the pendulum.
Remove the pendulum from the cuckoo clock by lifting it up and away from the loop in the suspension rod. If necessary, use a flashlight to view the loop and the hook at the end of the pendulum shaft.
Slide the wooden leaf on the pendulum shaft up if the clock was running slow and down if it was running fast. Move the leaf in small increments in the required direction.
Hang the pendulum back onto the loop and set the hands to the correct time. Set the pendulum in motion and check its progress in 24 hours.
Stop the pendulum and check the time with the digital timepiece. Adjust the wooden leaf until accurate timekeeping is achieved. Replace the pendulum, adjust the hands to the correct time and set the pendulum in motion.
Stop the pendulum and remove it from the clock. Mark the position of the leaf on the back of the pendulum shaft with a pencil. Indicate the season with an "S" for summer or a "W" for winter depending on which season it is.
Hang the pendulum, pull the weights up and set the time.
If the cuckoo is near a heater vent, radiator or an air conditioner, it should be moved to a location where there are fewer temperature changes.