Some computer users prefer a trackball over the more common mouse for ergonomic reasons. There seems to be no conclusive evidence from studies performed to determine which type of pointing device works best for most applications. Application users are encouraged to test different devices, and to maintain proper posture and scheduled breaks for comfort. Some disabled users find trackballs easier since they only have to move their thumb relative to their hand, instead of moving the whole hand, while others incur unacceptable fatigue of the thumb. Elderly people sometimes have difficulty holding a mouse still while double-clicking; the trackball allows them to let go of the ball while using the button.