The object of this report is to acquaint the operator with the operational and technical aspects of the beam current integrator as well as the theory of the system operation. The design and operation of a beam current integrator are described, and the theory of operation is discussed. The instrument has two channels. The console channel is designed to measure the accumulation of charge received by a target during a period of a day no matter what the range used in the experimenter's channel. An analysis indicated that this unit will measure the accumulation of charge by a target to an accuracy of 0.1215% assuming that the constant error due to shorting the integrating capacitor is accounted for. The instrument is ranged to handle from 0.5 to 500 mu a of beam current. (M.C.G.)