A measure of the oil in a tank by finding the distance between the top of the oil and the top of the tank and subtracting this measurement from the tank height. Outage gauging is used on large storage tanks in which there may be several feet of heavy sediment in the bottom preventing the plumb bob on the gauge line from touching bottom. By measuring the distance from the top of the tank whose height is known, the height of the oil from the bottom can be easily arrived at. See lnnage Gauge.
