An electric power assisted steering system comprising an input shaft and an output shaft, an electric motor connected to the output shaft, at least two sensors including one or more of: a position sensor, a torque sensor, and a motor position, and a motor controller that causes the motor to apply an assistance torque as a function of the torque measured by the torque sensor, in which each of the sensors produces at least one output signal represented by a stream of digital samples captured at discrete times, and in which the apparatus further comprises: processing means arranged to process together the output signals from both processing units to produce at least one further signal. At least one sample value of each output signal is marked with a time stamp indicating the time at which the sample was created, and in which the processing means corrects each of the time stamp samples before or during the processing of the samples to reduce errors that may occur due to differences in the times at which the samples were created.