English: A bimetallic temperature compensated balance wheel from an early 1900s pocket watch. 1.8cm diameter. The rim is made of two bimetallic semicircular arms, composed of a layer of brass on the outside fused to a layer of steel on the inside. As the temperature increases, the arms bend slightly inward, causing the balance to oscillate faster, to compensate for the thermal loss of elasticity of the spring. Moving opposing pairs of weights nearer the ends of the arms (1) increases temperature compensation. Unscrewing pairs of weights near the spokes (2) slows the oscillation rate.