A system and method for measuring the profile of an external surface of a part is provided. The system includes a source of light that directs light onto a region of the external surface of the part. The system also includes a linear, light-sensitive sensor, and a lens used to image locations within the region onto the sensor. The source of light and the sensor are located substantially within the same plane such that the sensor detects substantially only light scattered, diffracted, or reflected from the region and travelling substantially within the plane. The system additionally includes a re-positionable mirror that re-directs the light emitted from the source of light to the plurality of locations within the region and re-directs light scattered, diffracted, or reflected from the plurality of locations within the region to the lens and the sensor. An automatic gain control system which controls the output power of the source of light to thereby avoid saturating the exposure of the sensor may also be included in the above system. Further, a spring which functions as a low-pass filter may be used to couple the motor to the shaft of the rotating mirror. In another embodiment, a re-positionable polygon mirror system comprising standoffs with tangs which restrict the outside reflecting mirror surfaces to pre-aligned planes during rotation of the polygon mirror system is disclosed. A fail-safe eye safety technique is also disclosed which controls the power to the source of light. Even further, an optical scanning system is disclosed which utilizes bi-cell photo-detectors to determine the angular position of the source of light with high precision.