Abstract: A control system for variably operable devices, such as spotlight systems (16) to follow the movements of a performer (12) over an area, derives control data from a tracking head (14) which follows the movements of the performer (12). The tracking head (14) may be operated manually to follow the performer. A frame of reference (10) is set up over the area (10A), the frame of reference including at least four calibration points (1, 2, 3, 4), any three of which are not collinear. The frame of reference (10) also includes a reference point of origin (C). Prom the X, Y, and Z coordinates of the tracking head with respect to the calibration points and from the pan and tilt angles of the tracking head, control commands for the variably operable apparatus are computed in real time.