Abstract: A system for measuring the rotation of a shaft without direct mechanical connection to it uses a digital system to maintain a second shaft that connects to a cylindrical chart recorder in a constant angular position relationship with the measured shaft. Two limit switches on the recorder shaft sense the rotation of a reference point on the measured shaft beyond a range defined by the location of the limit switches. A stepper motor driven by digital power supply incrementally rotates the recorder shaft to move a reference point on the recorder shaft back into alignment with the reference point on the measured shaft. A digital counter controls the number of pulses supplied by the power supply to stop the recorder shaft in the aligned position.