Complex sentence: SQUIDs, or superconducting quantum interference devices, measure extremely small magnetic fields; they are very sensitive vector magnetometers, with noise levels as low as 3 fT/Hz 0.5 in commercial instruments and 0.4 fT/Hz 0.5 in experimental devices.
Split into simpler sentences: SQUIDs, or superconducting quantum interference devices, measure extremely small magnetic fields. They are very sensitive vector magnetometers, with noise levels as low as 3 fT Hz-½ in commercial instruments and 0.4 fT Hz-½ in experimental devices.