This is simply adjusting the regulator (an adjusting lever usually with a S slow or F fast range of setting-see images below) so the watch keeps accurate time in the position that it is in at the time of regulation (i.e.dial up (DU), pendant up (PU)). A timing machine is use in order to make adjustments rapidly. This is why the acronym COR (Clean, Oil, Regulate) is used as opposed to COA. Even though the watch has be regulated, it still will run at different rates in different positions. The task in regulation is to adjust it so that the average running rate is as close to a zero error in 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 personal error). An owner, if so inclined, may carefully nudge the regulator with a toothpick in order to make fine adjustments. Note, however, that the more accurate regulators are adjusted by a threaded component, and is more difficult to adjust. 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), adjusting the hairspring, and even shaping the balance pivots and adjusting how the hairspring is attached to the balance wheel.
The three critical adjustments are for position (as defined above, see accuracy), 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 reasonably constant in two to three positions (for a pocket watch dial up, pendant up, pendant left/right) as these are the most common positions the watch would encounter either in the pocket, or on a table at night. High grade watches are adjusted to five positions or more.