> Magnetometer <

Disturbances in the Earth's magnetic field may be caused by the presence of metal or perhaps by having the natural magnetic alignment of soils disrupted.  In any case, a magnetometer is an instrument which may measure and record these fluctations.  Applications include locating missing metal - such as the buried well stem shown in the example below.  

In the above example we were tasked with locating a well-stem long since lost as it was paved over some time ago.  In this case the magnetometer (total magnetic field) registered a tight, large anomaly on the eastern edge of the parking lot, validated with a pin finder, while the EM31-inphase, a sometimes metal detector, did not register much of an anomaly. The orientation , surrounding medium and depth of object all play a large role in instrument response.