A stroboscope or strobe is an instrument used to make moving objects appear stationary. When a rotating object is viewed with the stroboscope its frequency can be measured. Stroboscopes can be used in manufacturing to monitor the level of stress on machinery in motion, and they can also be used as a timing light to set ignition timing of combustion engines. Doctors may use videostroboscopy to record and evaluate the function of the vocal cords, or larynx, in people with voice disorders.