The equivalent circuit is a circuit for an electrical activity of a quartz crystal unit operating at its natural resonant frequency. The C0, or shunt capacitance, represents the capacitance of the crystal electrodes plus the capacitance of the holder and leads. R1, C1 and L1 compose the "motional arm" of the crystal, and are referred to as the motional parameters. The motional inductance, L1 represents the vibrating the vibrating mass of the crystal unit. The motional capacitance, C1 represents the elasticity of the quartz and the resistance, R1 represents bulk losses occurring within the quartz.