The magnetic section of the TriField meter has three field-detecting coils pointing in the X, Y, and Z directions. A unique network combines the three coil outputs nonlinearly to approximate a true magnitude. TriField is a registered trademark of W.B. Lee. Most often, this is caused by magnetic fields, which come largely from unpaired internal wiring. Other magnetic sources include video displays, motorized clocks and other equipment, electric blankets and heaters, fluorescent lights and light dimmers, and the transformers that are inside consumer devices.
Magnetic field is difficult to shield, but sheet steel is somewhat effective.
A few areas in most homes read HIGH in the electric field setting. These include areas near improperly grounded equipment, the front of video screens, and fluorescent lights. You can greatly reduce the strength of an electric field just by placing your hand in front of the source. This effect can be seen using a TriField meter. This was designed as a more general electromagnetic measurement tool.