Abstract: A region of a glass bottle is inspected for flaws or checks by scanning the region with a light beam. The passage of a flaw or check through the beam causes a fluctuation in the intensity of the light beam at two spaced apart locations. At each location, a sensor senses the fluctuation in beam intensity caused by the flaw or check. A difference amplifier generates a difference signal based on the sequential detection of the fluctuation in intensity of the light beam at the two locations. The difference signal is rectified and inverted. The inverted difference signal is rectified and combined with the rectified difference signal to produce a combined signal. If the combined signal exceeds a predetermined threshold value within a predetermined time interval, a reject signal is generated to operate a mechanism which removes the bottle by conventional means.