This present specification provides, amongst other things, an electro-optical monitoring system for obtaining a once-per revolution signal based on the surface reflection of a rotating device that mandates non-contacting sensor input in potentially hostile environments. The system can use optical and electronic sections to illuminate and detect surface reflections from the rotating surface using existing mounting locations on the periphery of the machine to be measured. The electronic portion is configured to determine a unique mark as the once-per-revolution marker or allow an attending operator to assign a specific marker based on the observed reflected pattern. The optical portion consists of a light source, receiver, and optics that allow for focused and directed light paths.