This Armco Rod String Oilmaster Pump Bore Unit Fluid Bbls Calculator Slide Rule dates back to 1965 and is an original piece of Gas & Oil advertising. The multi-colored slide rule is designed to calculate fluid barrels and is branded by Armco. It is in the used condition and has not been modified. The item was manufactured in the United States and is a unique addition to any collection of Gas & Oil memorabilia.