Quantum Design does not incorporate a field sensor such as a Hall sensor in its instruments. The magnetic field reported by the SQUID VSM is based on the current that is being generated in the magnet power supply (if the magnet is charging), or the last current that was sourced from the power supply when it was connected to the magnet (if the QuickSwitch on the magnet has been closed). The magnet power supply current is translated into a magnetic field using a constant field-to-current conversion factor (or “B/I ratio”) for that given magnet. This yields a magnetic field value that is very accurate at higher fields (above about 1 tesla).