One effect that is interesting is the precession of organic (kerosene) molecules in a proton procession magnetometer. Ever time a square wave cycle is imposed on the hydrocarbon using a wrapping coil the protons align the the coil. When the square wave amplitude drops to zero the protons return to align with the Earth's magnetic field. But they don't snap back immediately because they are spinning. Instead they proceed back, and the precession can be read on the same coil as an imposed decaying sine wave. The stronger the Earth's field, the faster the precession takes place. Using a crystal oscillator as a reference the Earth's field can be read to 1 part in 50,000 (lambdas). Submarines sometimes use these measurements of known magnetic fields to navigate through undersea mountain ranges.