We developed a new method that can diagnose damage on a gear tooth surface using a laser beam without a rotary encoder. The method procedure is as follows: 1) The tooth bottom. the tooth tip and their two median values are detected using the differential values of the laser reflection data. 2) The gear rotation speed is calculated with these four positions. https://www.roneverhart.com/1915-Old-Taylor-Bourbon-Bottled-1933-Prohibition-Bottling-Quart-low-fill/