An open frame type with double slides, for gauging alcohol content, made from boxwood & brass and has brass pin inserts at the gauge points, there are no makers marks I can find. The measurements IMG & IMB dates the rule between 1824 & 1880. There are also scale markings on both edges of the rule. The two slides move easily the rule is straight and measures 12 1/2” long by 1 7/8” wide with a thickness of 1/4”.
Price is inclusive of postage to mainland U.K.