Expert: Martin Meyer - 12/20/2007

Question
I have a brass and glass case French Japy Frere regulator clock with an adjustable mercury pendulum. I adjust the pendum up or down to increase or decrease the speed and it is still either too fast or too slow. There is a small squire rod sticking out of the face above the 12. I am wondering if it is a fine speed adjustment device, and if so, what direction should I move it to make the clock go faster.  Would moving it left would adjust the speed faster and rotating it to the right would adjust the speed slower? How much should it be turned or used? Thank you.

Answer
Hi James,
    The shaft near the 12 is for regulating. For most clocks,  turning it clockwise will make the clock run faster. You should turn this shaft in small increments, only one or two half-turns at each adjustment. The nut on the bottom of the pendulum can also be used for regulating; this nut should be turned in even smaller amounts, to the right (raising the pendulum disk) to make the clock go faster.
    Mainspring clocks always run slightly faster when fully wound, and a little slower toward the end of the week. So you should wind all mainsprings fully, as far as they will go, then make the regulation adjustment. Watch the clock for the full week, then make another adjustment after fully winding. Otherwise, you will be caught in a cycle of too fast and slow from making over-adjustments.