Square Ullage slide rule (with added engineering data and scales on brass sliding pieces) by "Edwd. Roberts, Maker in Dove Court in Old Jewry, London" 9" x 1 1/8" x 7/8", c. 1780

Square Ullage slide rule by "Edwd. Roberts, Maker in Dove Court in Old Jewry, London" c. 1780. Excise rules were used from the late 17th century to calculate the quantity of liquor in a barrel when full, and a ullage rule can be used with a gauging rod to find the volume when the barrel is partly empty. The calculations were very complicated.