A controlling method and a device are disclosed to calibrate a pointer assembly of an air-core meter. The pointer assembly of the instrument includes a calibrating magnet, a cosine coil, a sine coil and a pointer. According to the polarity of the return-to-zero magnetic field established by the calibrating magnet, a compensating voltage is imposed on the cosine coil or the sine coil or both under either a voltage driving mode or a current driving mode. The compensating voltage establishes a compensating magnetic field to cancel the return-to-zero magnetic field. Therefore, without modifying the structure of the pointer set, the pointer has good linearity and is not affected by the calibrating magnet.