The poising of balance wheels is typically performed at the factory. Re-poising of the balance wheel is often necessary when a balance staff is replaced or there are other changes to components. The object of poising the balance wheel is to locate the center of gravity at the center of the staff. This is accomplished by removing weight from locations at the greatest diameter until the weight is evenly distributed. Static poising is performed on a balance that is clean, true in the round and flat, and with hairspring and collet removed. Fine adjustments can be made via dynamic poising with the balance installed in the watch. Care must be taken to ensure the hairspring is properly adjusted so as not to remove material from the balance wheel to compensate for errors in hairspring adjustment.
When poising a balance wheel (either statically or dynamically), it should be performed in a clean and neat fashion. As little weight as necessary should be removed; and when possible, weight should be removed from only one point on the balance wheel. Any burrs raised during the drilling operation should be removed.
On modern balance wheels without screws, weight is removed by drilling a hole in the underside of the balance rim. This hole MUST NOT penetrate beyond either edge of the rim.
On modern free-sprung balance wheels with regulating devices (Micro-Stella, Gyromax, etc.), care must be taken to insure the weights are distributed evenly before undertaking poising. Sometimes this is best accomplished by moving them to their extreme inner position. Regulating screws or nuts should NOT be used for adjusting poise.
If marks are made with ink to mark the location of the roller jewel or hairspring collet when replacing the staff, they must be removed before installing the balance in the watch.