Regulating is moving the regulator pointer to fast or slow adjusting the rate. A watch may run at different rates in different positions. The task of regulation is to modify it so that the average running rate is close to a zero error between the most common positions. Thus, the correct setting for the regulator will be slightly different for each owner, depending on how the watch is worn or carried (this is sometimes referred to as personal error). In the shop, a watchmaker uses a timing machine to adjust the rate quickly.
If your watch is not keeping precise time, you can adjust the regulator yourself. A slight nudge toward the F (or fast) will speed the watch up, and toward S (or slow) will slow it down. Then let the watch run for a few days to see how much the rate was affected. Higher grade watches utilize a micrometer regulator and afford more fine control via a small screw. These are a bit more difficult to adjust, as the screw can be tight, and the small screwdriver can easily slip. If in doubt, let an expert adjust the regulator (see images below).
Adjusting a watch involves procedures that include ensuring the balance wheel is ‘balanced’ (poised), reshaping the hairspring, shaping the balance pivots, and changing how the hairspring is attached to the balance wheel.
The three critical adjustments are for position, temperature (the ability to keep good time over a range of different temperatures), and isochronism (the ability to keep an even rate over the life of one spring wind, typically 24 hours). An un-adjusted watch should run at a reasonably constant rate in two to four positions. The primary positions for a pocket watch are stem-up, face-up, stem right, and left. Medium grade wristwatches are adjusted for stem down-left-right and face up. High-grade wrist and pocket watches are adjusted to vary no more than 5-10 seconds between six positions.