Abstract: A combined torque and angular position detector includes two disks rotatable about a common axis. Relative angular displacement of the disks results from torque applied thereto. Each disk has a number of regions of differing optical transmissivity and these control the transmission of optical radiation from a source to an array on which an image of the regions of the disks is formed. A data processor processes image intensity data and determines the angular positions of the disks and their relative displacement. Alternative arrangements are descried in which positional information is derived by providing one disk regions of intermediate transmissivity of width varying around one disk, by having the regions of lesser transmissivity of width varying around one disk or by arranging combinations of regions of several different widths around one disk.