The single detector-bottle free-precession magnetometer was adapted for measuring weak magnetic field gradients by comparing the signals from two detector-bottles. The electronic circuits for handling two decaying waveforms  were developed. The single detector-bottle magnetometer was used by external organisations for measuring the earth’s total magnetic field on the sea-bed and at altitude from a Skylark research rocket. The gradiometer was used for detecting weak magnetic field anomalies due to buried plastic mines and archeological remains. External organisations used the derived data from the single and double detector-bottle free precession magnetometers to postulate certain geophysical and geomagnetic theories.