- Wrap a steel needle with insulated wire;
- Connect the wire with power supply operating under constant current mode. A small resistor of 2Ohm is connected in serial with the coil.
- Fix the compass on the table, record the initial position of compass needle;
- Put the tip of the steel needle at a fixed position (as marked in the figure), perpendicular with the initial orientation of compass needle;
- Read the deflection angle of compass needle;