An electronic measuring device is described that can include first and second input inductors connected in series. A shunt inductor is connected in parallel with the second input inductor. Optionally, an additional shunt inductor may also be used in parallel with the first input inductor. The first and second input inductors are inductively coupled to first and second SQUIDs which are in turn inductively coupled to first and second feedback inductors. First and second SQUID controllers are connected, respectively, to the first and second SQUIDs as well as the first and second feedback inductors. The first and second SQUID controllers are also connected to a processor. The processor is operable to process the output of the first and second SQUID controllers to detect unlocking events in the output of the first SQUID controller.