the gyromax is the trade name for an adjustable mass (or adjustable inertia) balance wheel used in patek philippe wristwatches. instead of weight adjustment screws on the outside of the rim, as in traditional balances, the gyromax has turnable weights recessed into the top of the rim. the advantages claimed for this design are that, without projecting weight screws, the diameter of the balance can be increased, giving it a larger moment of inertia, and that it has less air resistance.