Multi-channel developments were of particular use to aircraft which really needed a minimum of three control dimensions (yaw, pitch and motor speed), as opposed to boats which can be controlled with two or one. Radio control 'channels' were originally outputs from a reed array, in other words, a simple on-off switch. To provide a usable control signal a control surface needs to be moved in two directions, so at least two 'channels' would be needed unless a complex mechanical link could be made to provide two-directional movement from a single switch. Several of these complex links were marketed during the 1960s, including the Graupner Kinematic Orbit, Bramco, and Kraft simultaneous reed sets.