As mentioned earlier, these rates also depends on the quality of the main spring, gear train, and escapement. After adjustment, the rate of the watch still has a residual variation, which is small for a high-quality movement. It is a relatively simple procedure that entails changing the effective length of the hairspring via the regulator, or changing the center of mass of the balance wheel to change the absolute rate. Accuracy still varies in actual use, as a watch is never perfectly adjusted, so further regulation may be needed after purchase or service to suit the user s life-style. In summary, adjustment renders a watch rate as insensitive as possible to the rigors of normal use.
Regulation is a simpler process that matches the watch rate to the rate of a reference clock.
Now let s turn our attention to the much abused term on TimeZone, accuracy, and its often neglected but more important twin, precision, and see how they relate to adjustment and regulation. So strictly speaking, a watch is accurate when it keeps time with respect to a reference clock, the same way that a shooter is accurate when his bullet hits the bulls-eye, or close to it, to borrow Graiche s analogy. This usage actually violates the definition of the word accuracy, and runs counter to its usage in science, engineering, and other fields as well. Accuracy must relate to a comparison with a reference, not to consistency or reproducibility, which is strictly the domain of precision. This raises the question on what to do to avoid confusion when people of different experience communicate about watches.