Few clocks of either the pendulum or the alarm-clock type are made with devices to compensate for changes in temperature, and as these changes will alter the rate, it is desirable to keep the clock in the part of a room where its temperature will be most constant. Even with the best conditions in this respect, it will be necessary to regulate the clock's rate frequently on account of the changes of temperature with season 01 with the conditions of heating or cooling of the room. A rise of temperature will lengthen the pendulum rod and make the clock run more slowly. It will be necessary, therefore, to raise the pendulum bob by turning the supporting nut, unless an adjustment device is provided by which a contact point on the suspension spring at the top of the pendulum can be changed. This is done by turning a key to right or left in a small keyhole in the face of the clock, usually near the upper part of the dial. This has the effect of shortening or lengthening the pendulum.

In the alarm-clock type, the regulation is done by moving a small lever, usually at the back of the clock, which engages with the hairspring on the balance wheel, and so decreases or increases the effective length of the spring, thus controlling the time of a vibration of the balance. The lever should be moved toward the letter "S" when one wishes to make the clock run more slowly and toward "F" when it should run faster. The same rule applies in the regulation of a watch.

When regulating a pendulum clock by the key device, the key should be turned overhand toward the letter "S" or "F," according as one wishes to make the clock run more slowly or faster. If there are no indicating letters ("F" and "S") provided, the usual rule is to turn the key in the direction the hands move to make it go faster or counterclockwise to make it run more slowly.

The amount of movement required to correct the rate must generally be found by trial. Thus, if the clock gains five minutes a day, and one turns the key of the regulator two revolutions toward "S," or moves the lever of an alarm clock two divisions toward "S," and the clock then loses three minutes a day, one can obtain nearly zero rate by turning the key three-quarters of a revolution back toward "F" or by moving the lever three-quarters of a division back toward "F." In some pendulum clocks there may be some motion lost in reversing the regulation, and this should be taken into account in estimating the amount to move the regulator.

To correct the striking of a clock.

While some clocks of a more recent type have the hour and minute pinions and the striking mechanism so geared together that it is almost impossible for the clock to strike wrongly, this frequently happens with other types of clocks. This difficulty can be remedied easily in the latter case by several methods. One method, which can be used in case the hour hand is held in position on its shaft by friction only, is to move the hour hand backward or forward an hour or more as may be necessary to make the hour indicated by the clock-face agree with the striking mechanism, pressing the hour hand tight on its shaft afterwards, as described above. Then the clock should be set to correct time by moving the minute hand around the dial the necessary number of times, allowing the clock to strike the full amount each time the hand passes the XII point before approaching that point again. This method is especially convenient when the clock strikes one or two strokes less than it should. When it strikes more strokes than it should, the same method may be used, or the minute hand may be turned ahead rapidly so that it will again pass through the XII point while the clock is still striking for the previous hour. By so doing the striking mechanism is not released to strike the following hour, and thus an hour is gained in the face indication of the clock compared with the striking. This may be repeated as many times as the number of strokes by which the striking mechanism was in error. The clock may then be set to correct time in the usual way, allowing it to strike the full amount on each passage of the XII point, or the clock may be stopped for as many hours as it is fast, until again it indicates the correct hour, when it can be started and set correct without the necessity of striking all the nine, ten, or eleven hours that may have intervened.

Some clocks have a lever in the movement - an extension of the striking mechanism release arm or shaft - which can be moved up or down to release the striking mechanism and allow it to strike as many hours as are necessary to bring it into agreement with the indication of the hands. Or, if a special lever for the purpose is not provided, it is sometimes easy, on opening the door to the works of the clock, to find the release arm itself and by raising it accomplish the same result.