Measurement Source used as active by the object. Possible values for this property are 1: SCADA, 2: Operator (default), 3: Control Center, 4: Billing, 5: Calculated, 6: Database, 100: Topological Processor, 101: Power Flow, 102: State Estimator, 103: Load Shedding, 104: Distribution Load Modelling, 105: Self-Healing, or 106: External Reader. The selected Source type must exist in the Measurement to be set as active. It is not possible to select types 100, 101, 102, 103, 104, 105, or 106 (Electrical Study outputs) if the StudyInputSource property is set to 0 (ActiveSource). In case the selected Source is deleted, this property assumes a value of 2 (Operator).