How does it identify the north and south poles of a permanent magnet? Simply press and hold the black oval button. Then, place the tip of the detector near the surface of the magnet. If it is the North Pole, the Red LED will glow. If it's the South Pole, the Green LED will glow. It's just that simple. And if the button is held and the unit is moved around the surface of the magnet....you can see the transition from one pole to another. This pole identifier is guaranteed to be 100% accurate. It can be used for rare earth magnets such as neodymium magnets, SmCo magnets, AlNiCo magnets, Ceramic magnets, refrigerator magnets and most other magnets. Applications Pole detection of permanent magnets Measurement of stray magnetic fields in packaging Coil testing Post-magnetization polarity checks Helps with the following tasks: Electric motor assembly Installation of magnetic clamping blocks Error Analysis Multipole quality control Pole detection of therapy magnets Dimensions: approx. 5.6" x 0.9" x 0.8", measuring side 1/2" x 1/2" Weight: approx. 0.08 lb with batteries Display: two LED display (green= south, red=north) Sensitivity: ±17mT (170Gs) on/off hysteresis Operating temperature range: -10°C ~ +50°C Storage temperature: -20°C ~ +70°C Battery: 4 x 1.5v button cells (included)