Patent ID: 8100579

Claim:
A balance wheel for use in conjunction with a balance spring in a mechanical oscillator system in a horological or other precision instrument, the balance wheel comprising: a body of non-magnetically sensitive material having a linear coefficient of thermal expansion of 9×10 −6 K −1 or less; and a plurality of non-magnetically sensitive compensating appendages arranged in equipoise on the body, each appendage comprising a mass element attached to the body via a compensation structure, the compensation structure being arranged to move the mass element relative to the centre of mass of the body with an increase or decrease in temperature; wherein the mass element is adjustably mounted on the compensation structure to permit the position of the centre of mass of the mass element relative to the compensation structure to be altered; the compensation structure is adjustably mounted on the body to permit a direction of movement of the mass element relative to the centre of mass of the body with an increase or decrease in temperature to be altered; and expansion or contraction of each appendage with an increase or decrease in temperature is arranged to move its centre of mass relative to the centre of mass of the body to alter a mass distribution of the balance wheel relative to its centre of mass to compensate for a change in the elasticity of the balance spring caused by the increase or decrease in temperature.