Various embodiments include a reflectometer and a reflectometry system for monitoring movements of a substrate, such as a silicon wafer. In one embodiment, a reflectometry system monitors and controls conditions associated with a substrate disposed within a process chamber. The process chamber includes a substrate-holding device having an actuator mechanism to control movement of the substrate with respect to the substrate-holding device. The reflectometry system includes a light source configured to emit a beam of light directed at the substrate, collection optics configured to receive light reflected from the substrate by the beam of light directed at the substrate and output a signal related to one or more conditions associated with the substrate, and a processor configured to process the signal and direct the actuator mechanism to control the movement of the substrate with respect to the substrate-holding device based on the signal. Other devices and methods are disclosed.