Measurement Source used as active by a Discrete Measurement. Possible values for this property are 1 - stScada: SCADA, 2 - stOperator: Operator (default), 3 - stCCLink: Control Center, 4 - stBilling: Billing, 5 - stCalculated: Calculated, 6 - stDatabase: Database, 100 - stTopologyProcessor: Topology Processor, 101 - stPowerFlow: Power Flow, 102 - stStateEstimator: State Estimator, 103 - stLoadShedding: Load Shedding, 104 - stDistLoadModelling: Distribution Load Modeling, 105 - stSelfHealing: Self-Healing, or 106 - stExternalReader: External Reader. The selected Source type must exist in the Discrete Measurement to be set as active. Users cannot select types 100, 101, 102, 103, 104, 105, or 106 (outputs of Electrical Studies) if the StudyInputSource property is set to 0 (zero, ActiveSource). In case the selected Source is deleted, this property assumes a value of 2 (two, Operator).