Abstract: A position indication derived from the output signal of an engine demand device sensor is compensated for errors which tend to expand or contract the range of such output signal. The signal is compared to previously stored upper and lower reference values nominally corresponding to the limit positions of the demand device, and the position indication is derived in accordance with such comparison. The compensation is achieved by altering the previously stored upper and lower reference values at the initiation of each period of vehicle operation, in a sense to contract the range of output signals defined thereby, and by replacing the upper or lower reference values with the sensor output signal value during the ensuing period of vehicle operation if the sensor output signal value is greater or less than the upper or lower reference values, respectively.