Adjustment
Movements that are marked to be "Adjusted" may have a variety, or combination, of features. One has to read the factory specification for any given movement grade to discover just what level of adjustment is being claimed. High grade watches built after 1905-1908 may be marked with specific adjustments. This is especially true for watches intended for use in railroad time service. The purpose of all of these features is to keep the balance wheel (the wheel that spins back and forth rapidly), as nearly as possible, oscillating at a consistent rate. The consistency of the rate of oscillation of the balance (wheel) is the timekeeping quality of the watch.
Temperature Compensated Balance (wheel)
A balance wheel that is temperature compensated has the rim made of two dissimilar metals. There are usually two arms (spokes) from the hub supporting the rim and there is a slot cut in the rim just past each arm. This forms two rim segments having one end supported by the arm and the far end free to move. These slots, and the two colors of metal in the rim, are identifying characteristics. As the temperature increases, lessening the power of the hairspring (the spring coiled inside of the balance wheel), the far ends of the rim segments deflect inward. As temperature decreases, the segment ends relax, moving outward, as the hairspring strength increases. The action is much like an inexpensive thermostat in the home. This movement of the rim segments changes the moment of inertia of the balance wheel, compensating for the alteration in the hairspring strength.
Adjustment to Temperature
This is sometimes referred to as adjustment to heat and cold. It requires a temperature compensated balance. The balance has pairs of screws (180 degrees apart) set into the rim. These give the balance mass, which sets the basic rate at which it oscillates. One pair may be the meantime screws, used to bring the rate deviation to minimum (with the regulator in its center position) after all of the other adjustments have been made. The locations of most of the pairs of screws (each pair is 180 degrees apart) on the balance wheel rim are chosen to provide the best match of change in moment of inertia to change in hairspring strength (there are extra pairs of holes so that the screws may be moved to the best possible positions). The object is to keep the balance wheel oscillating at the same rate over the specified temperature range.
Adjustment to Position
The next level is adjustment to position. This is adjustment to maintain the same rate of balance wheel oscillation, regardless of which of the specified positions the watch is in. There are a total of six positions. Unfortunately, the number or the positions to which the watch is adjusted isn't specified for most watches built prior to 1905-1908. Typically, unspecified adjustment to position means adjustment to three positions, but there are a number of instances in which it means five positions. Adjustment to three positions most likely means stem up, stem at the 3 o'clock position and stem at the 9 o'clock position.
Adjustment to Isochronism
Then, there is adjustment to isochronism. This is accomplished by the design and adjustment of the hairspring (the spring coiled inside of the balance wheel). The power output of the mainspring (the spring that is wound when winding a watch) tends to decrease as it unwinds over the course of the day. This causes the balance wheel to rotate through a greater rotational angle when the mainspring is just wound and a lesser angle when the mainspring needs winding. A watch adjusted to isochronism oscillates the balance wheel at the same rate throughout the specified length of run between windings of the mainspring, regardless of how far in each direction the balance wheel rotates. This length of run is typically 30 hours for earlier watches and 42 hours for post World War I watches of better quality. However, mainsprings whose power output were nearly constant over the first 20 hours after a full winding were supplied in higher grade watches starting in the late 1920's. The need for adjustment to isochronism lessened with the application of these mainsprings.
Movements that are marked to be "Adjusted" may have a variety, or combination, of features. One has to read the factory specification for any given movement grade to discover just what level of adjustment is being claimed. High grade watches built after 1905-1908 may be marked with specific adjustments. This is especially true for watches intended for use in railroad time service. The purpose of all of these features is to keep the balance wheel (the wheel that spins back and forth rapidly), as nearly as possible, oscillating at a consistent rate. The consistency of the rate of oscillation of the balance (wheel) is the timekeeping quality of the watch.
Temperature Compensated Balance (wheel)
A balance wheel that is temperature compensated has the rim made of two dissimilar metals. There are usually two arms (spokes) from the hub supporting the rim and there is a slot cut in the rim just past each arm. This forms two rim segments having one end supported by the arm and the far end free to move. These slots, and the two colors of metal in the rim, are identifying characteristics. As the temperature increases, lessening the power of the hairspring (the spring coiled inside of the balance wheel), the far ends of the rim segments deflect inward. As temperature decreases, the segment ends relax, moving outward, as the hairspring strength increases. The action is much like an inexpensive thermostat in the home. This movement of the rim segments changes the moment of inertia of the balance wheel, compensating for the alteration in the hairspring strength.
Adjustment to Temperature
This is sometimes referred to as adjustment to heat and cold. It requires a temperature compensated balance. The balance has pairs of screws (180 degrees apart) set into the rim. These give the balance mass, which sets the basic rate at which it oscillates. One pair may be the meantime screws, used to bring the rate deviation to minimum (with the regulator in its center position) after all of the other adjustments have been made. The locations of most of the pairs of screws (each pair is 180 degrees apart) on the balance wheel rim are chosen to provide the best match of change in moment of inertia to change in hairspring strength (there are extra pairs of holes so that the screws may be moved to the best possible positions). The object is to keep the balance wheel oscillating at the same rate over the specified temperature range.
Adjustment to Position
The next level is adjustment to position. This is adjustment to maintain the same rate of balance wheel oscillation, regardless of which of the specified positions the watch is in. There are a total of six positions. Unfortunately, the number or the positions to which the watch is adjusted isn't specified for most watches built prior to 1905-1908. Typically, unspecified adjustment to position means adjustment to three positions, but there are a number of instances in which it means five positions. Adjustment to three positions most likely means stem up, stem at the 3 o'clock position and stem at the 9 o'clock position.
Adjustment to Isochronism
Then, there is adjustment to isochronism. This is accomplished by the design and adjustment of the hairspring (the spring coiled inside of the balance wheel). The power output of the mainspring (the spring that is wound when winding a watch) tends to decrease as it unwinds over the course of the day. This causes the balance wheel to rotate through a greater rotational angle when the mainspring is just wound and a lesser angle when the mainspring needs winding. A watch adjusted to isochronism oscillates the balance wheel at the same rate throughout the specified length of run between windings of the mainspring, regardless of how far in each direction the balance wheel rotates. This length of run is typically 30 hours for earlier watches and 42 hours for post World War I watches of better quality. However, mainsprings whose power output were nearly constant over the first 20 hours after a full winding were supplied in higher grade watches starting in the late 1920's. The need for adjustment to isochronism lessened with the application of these mainsprings.
