How to Set the Timing or Beat on a Mantel Clock
First off make sure your clock/movement is level. I like to use a line level. You can get them for a couple of bucks at the local Home Depot.
Next get a piece of masking tape and put it below the movement. (See pic)
Draw an arrow where the pendulum hangs down. Now move the pendulum right until you hear it tick. Draw a line on the tape there. Now Move the pendulum to the left until you hear it tock. Now draw a line on the tape there.
Look at your lines in relation to the arrow. If the line on the left is further from the arrow than the line on the right bend the crutch (this is the metal wire that the pendulum runs through) slightly to the right. If the line the right is further away bend your crutch slightly to the left. Repeat the process above with marking the tape. Repeat this process until both lines are an equal distance from the arrow. Congrats! You have just set your timing/beat.
You know a clocks timing is correct when it runs with out the pendulum bob like in the video below: