Tremor is the most apparent and well-known sign.[1] It is also the most common; though around 30% of individuals with PD do not have tremor at disease onset, most develop it as the disease progresses.[1] It is usually a rest tremor, maximal when the limb is at rest and disappearing with voluntary movement and sleep.[1] It affects to a greater extent the most distal part of the limb, and at onset typically appears in only a single arm or leg, becoming bilateral later during the course of the disease.[1] Frequency of PD tremor is between 4 and 6 hertz (cycles per second).