Since the gyro axis and the normal to the loop are nearly perpendicular, the London flux through the pickup is proportional to the small misalignment angle, corresponding to a magnetic field of the order 10 -13 gauss. This flux is modulated at the roll frequency. Conservation of magnetic flux through the primary circuit is maintained by a current in the transformer's secondary circuit. The resulting output signal is a voltage proportional to that of the secondary current. With two pickups on each of four gyros, eight such voltages are digitized and recorded with 16-bit precision.
Magnetometer signals appear also at other frequencies.
Flux quanta trapped in the superconducting gyro rotors produce signals modulated at the spin frequency, around 125 Hz. Aberration of light from the reference star occurs both at the satellite's Earth orbital frequency and at the annual frequency of motion around the Sun. These aberrations are manifested as apparent precessions of the gyro axes at those frequencies. Also modulated at the satellite's Earth-orbital frequency and its harmonics are other effects, including periodic occultation of the reference star by the Earth. Absolute calibration of the magnitude of the gyroscope precession signal will be achieved by comparing it to the signals caused by aberrations of the reference star.