Vibration magnetometer is used for comparing

Vibration magnetometer is simple instrument which is used to find out the magnetic moment of a magnet or to compare the magnetic moments of two bar magnets. Here the magnet is made to oscillate and its time period is calculated, hence the instrument is called vibration magnetometer. It's time period is given by

                            $T=2\mathrm{\pi }\sqrt{\left(\frac{\mathrm{I}}{\mathrm{MH}}\right)}$