 They also have applications in heart beat monitors, weapon systems positioning, sensors in anti-locking brakes, weather prediction (via solar cycles), steel pylons, drill guidance systems, archaeology, plate tectonics and radio wave propagation and planetary exploration.Depending on the application, magnetometers can be deployed in spacecraft, aeroplanes ("fixed wing" magnetometers), helicopters ("stinger" and "bird"), on the ground ("backpack"), towed at a distance behind quad bikes ("sled" or "trailer"), lowered into boreholes ("tool", "probe" or "sonde") and towed behind boats ("tow fish").Magnetometers are used to measure or monitor mechanical stress in ferromagnetic materials.