Calibration is to eliminate geographical errors.
The common calibration method is to calculate and calibrate with the previously saved position and current position. According to two different situations of magnetic declination, the direction of dial correction is clearly judged. If the magnetic north deviates to the east of the coordinate north, the coordinate azimuth is greater than the magnetic azimuth.
After aiming at the target, the dividing line of dial 0 should be moved clockwise to increase the count of the north end of the magnetic needle finger; If the magnetic north deviates to the west of the coordinate north, the coordinate azimuth is less than the magnetic azimuth. At this time, the 0-degree dividing line of the dial should be moved counterclockwise to reduce the reading at the north end of the magnetic needle after aiming at the target. After the magnetic compass is corrected by the circle, the coordinate azimuth of the straight line can be measured directly.
Extended data:
Principle of magnetic compass
The geomagnetic north and south poles do not coincide with the geographical north and south poles, and the direction of the free floating magnetic needle has a deviation angle from the direction of the geographical north and south poles (true meridian), that is, the magnetic declination angle (also called magnetic difference). In the specially drawn navigation chart, the magnetic difference correction in various places is marked. By adding the magnetic heading reading to the magnetic difference algebra, the real heading of the aircraft can be obtained. The angle between the geomagnetic field intensity vector and the horizontal plane is called the magnetic dip angle.
The magnetic inclination is not equal everywhere, and the closer to the earth, the greater the magnetic inclination. At high latitudes, the horizontal component of geomagnetic field is very weak, which has little influence on the orientation of horizontally suspended magnetic rods. Therefore, the magnetic compass cannot be applied to the polar regions of the earth.
In the aviation magnetic compass, a pair of permanent magnetic rods are suspended under the floating ball, which is folded to keep the magnetic rods horizontal. The floating ball is supported on the jewel bowl with the shaft tip and suspended in floating liquid (ethanol, light kerosene or other compass oil) to reduce the friction with the supporting part. Connecting the magnetic rod and the floating ball is the azimuth scale ring.
The heading line reading indicating the nose direction relative to the azimuth scale ring is the heading of the aircraft. When the ambient temperature changes, the volume of floating liquid will expand and contract, so the expansion chamber is used to compensate. Due to the interference of the magnetic field formed by the steel components and electrical equipment on the aircraft, the magnetic bar will be stable in the direction of the synthetic magnetic field (compass meridian) of the geomagnetic horizontal component and the aircraft magnetic field horizontal component.
The deviation angle between the north direction of the compass and the magnetic north is called compass difference. The compass values of the same plane in different directions are not equal. In order to measure the magnetic heading of the aircraft correctly, a compass corrector is installed on the shell of the magnetic compass to generate an artificial compensation magnetic field that can be adjusted at will to weaken or offset the interference of the magnetic field of the aircraft. The magnetic compass should be installed on the machine with weak magnetic interference.
Baidu encyclopedia-magnetic compass