How to Read a Moon Phase Dial on a Grandfather Clock

Set the moon phase dial on your grandfather clock by turning it clockwise until a face is directly below the "15" on the top of the dial. That's where it should stand on a full moon.

Check a farmer's almanac to find out when the last full moon was, and count the number of days between then and now. Most moon phase dials on grandfather clocks turn twice a day; more modern ones may turn once a day. Regardless, you should feel a click whenever you turn the dial clockwise, marking that advance. From its position with the moon face directly below the "15," turn the dial clockwise a number of times equal to the days since the full moon if your dial turns once a day or two times that amount if your dial turns twice a day. Your moon phase dial is now set correctly.

Look at the shape of the moon on the moon phase dial. It may be partially or totally obscured by the round humps on either side of the opening. The portion of the face that is showing indicates the precise phase the moon is currently in: new, full, waxing or waning.

Examine the position of the top of the moon on the dial in relation to the numbers arranged above it. That figure is the number of days since the new moon. If the moon is waxing, subtract that figure from 15 to get the number of days until the full moon. If the moon is waning, subtract 15 from that figure to get the number of days since the full moon.