An apparatus and method provide logic for controlling a controllable device by distinguishing between an intended motion of a user and an unintended motion of the user. In one implementation, a computer-implemented method is provided to control a controllable device by distinguishing between a control movement and a non-control movement. The method receives spatial positions of a joint of a human appendage and a reference point disposed along the appendage and distal to the joint. The method determines whether a movement of the reference point about the joint is a control movement or a non-control movement, based on a comparison of direction of movement of the reference point and a direction of displacement between the reference point and the upper joint. A control instruction is executed when the movement is a control movement.