Apparatus includes a first Hall sensor having a first terminal, a second terminal, a third terminal and a fourth terminal and a second Hall sensor having a fifth terminal, a sixth terminal, a seventh terminal and an eighth terminal. A conductor connects the third terminal to the fifth terminal. A processor is configured to measure a first potential between the fourth terminal and the sixth terminal while transferring a first current from the first terminal to the seventh terminal via the conductor, to measure a second potential between the first terminal and the seventh terminal while transferring a second current from the fourth terminal to the sixth terminal via the conductor, and to determine a resultant voltage generated by the first and second Hall sensors in response to the first and second potentials.