If your clock is ticking away but its a little slow or fast, use this calculator to determine how much to shortern or lengthen the pendulum. You don't have to be too precise on the current length; if you have a fairly close figure, then the needed change will be close too.

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

Calculator

Change in Pendulum Length

Pendulum Measurements:

 Current Pendulum Length:

 in.

 cm.

How Fast or Slow is the Clock Currently?

Mins

Secs

Fast, or

 In 24 Hours:

Slow

 In 1 Hour:

Pendulum Beats:

Current

   Desired

Beats per Minute:

Beats per Hour:

(Override if you have a reading from an electronic timer;
the actual pendulum length will be displayed below.)

Results:

Current

   Desired

Pendulum Length:

 in.

 cm.

 

Needed Pendulum Chg:

 in.

 

 cm.

Tips

The center of gravity includes the mass of the pendulum bob and the pendulum shaft. However, with this calculation of determining the needed change in pendulum length it is really only important to measure the estimated center of gravity in exactly the same way each time.

Formula:

BPM = (141120 ÷ L_P)^½

where,

• BPM is beats per minute
• L_P is the pendulum length

This calculator, provided by Horology - The Index, is one in a series of repair calculations. This calculation may be used by anyone who wishes to adjust a pendulum clock to be faster or slower.