This is a nice clean, vintage, rotary slide calculator, marked "ABRASIVE COMPANY GRINDING WHEEL SPEED CHART". It has information on both sides, the front side rotates to calculate the based on the diameter of the wheel. A simple calculator to determine the surface speed in FT./MIN.. The back side is mostly advertising information for the "ABRASIVE COMPANY" a Division of Simonds Saw and Steel Co. Phila. Pa. U.S.A..