The most common presenting sign is a coarse slow tremor of the hand at rest which disappears during voluntary movement of the affected arm and in the deeper stages of sleep.[1] It typically appears in only one hand, eventually affecting both hands as the disease progresses.[31] Frequency of PD tremor is between 4 and 6 hertz (cycles per second). A feature of tremor is pill-rolling, the tendency of the index finger and thumb to touch and perform together a circular movement.[31][32] The term derives from the similarity between the movement of people with PD and the early pharmaceutical technique of manually making pills.[32]