Abstract: An automatic doubles and sheet thickness detector is disclosed that operates by comparing consecutive sheet materials that are delivered to a rotating drum.The consecutive sheet materials pass under two spaced apart rollers that are movably biased against the drum. If a sheet of greater thickness or a double sheet passes under one of the rollers, it will be displaced a greater distance from the drum surface than the other roller. This displacement is magnified by means of elongated pivot arms, which are attached to each roller. The magnified movement is detected by means of an optical arrangement comprising a light source, a photodetector, and a pair of mirrors. The mirrors are each secured to a distal end of a respective pivot arm. The light source casts a beam that reflects off each mirror towards the photodetector.