Pocket watches are intricate, miniature machines. A complex set of gears and wheels works in tandem with a spring that supplies the power. Pocket watches are carefully balanced to permit them to run in a variety of positions. Improper balance causes what is known as a "positional error." Positional errors result in timing discrepancies when the watch is held, or placed, at different angles. A positional error is one of the most common problems with pocket watches.
Open the pocket watch, and remove the pallet lever. The pallet lever is what controls the balance wheel by first holding, and then releasing, it.
Deliver a few puffs of air to the balance wheel using the watch blower. Examine the motion of the balance wheel. Does it move freely and regularly? Repeat the process of blowing air on the balance wheel while holding the pocket watch in a few different positions.
Tighten the balance wheel if it does not move freely. Sometimes the balance wheel rubs up against the underside of the center wheel. The balance wheel might also simply be wobbly.
Check for small obstructions if the balance wheel still does not operate correctly. Screws from other parts of the movement might be sticking out toward the balance wheel. Look for loose screws, and tighten if necessary.
Use the loupe to examine the balance staff. The balance staff holds the balance wheel, roller table, and hairspring. The pivots on the balance staff must be perfectly shaped and smooth, without evidence of scores, or lines.
Close up the pocket watch if it is working properly. If not, the balance staff, or some other part, will need to be professionally repaired or replaced.