Abstract: A discrete position encoder includes a plurality of detectors, arranged along a direction of motion or relative position between two objects, which are rendered responsive in either of two states by another member which is relatively movable with respect thereto, such as light beams established by light sources and optical detectors being interruptible by a vane. The vane is adjusted so that when the two objects are centrally aligned with each other, the two outermost detectors have a state opposite to other detectors. Two rows of detectors are provided to permit flexibility in designing the positional extent of detectable discrete positions. Exemplary decoding includes the decoding of as many fault states as acceptable decodable discrete position states. Embodiments with opposite detector states (ON/OFF vs OFF/ON) are disclosed.