Abstract: A controller has a stationary housing, a stem projecting from the housing along a stem axis, and a mount in the housing operatively engaging the stem and permitting same to tip relative to the housing about a center point in the housing generally traversed by the axis. An element carrying at least one emitter/receiver unit directs a beam generally radially of the center and another element carrying a field of interleaved reflective and less reflective regions is juxtaposed with the unit, spaced from the center, and impinged by the beam of the unit. One of the elements is fixed on the housing and the other of the elements is fixed on the stem so that on tipping of the stem about the center the beam is swept across the regions of the field.