If the deviation is more than 7 degrees, check coordinates of each Tracking Sensor, position of Tracking Sensor relative to cardinal directions, "magnetic variation" value (see Table 8. 2).
If all values are correct, however, the deviation is more than 7 degrees, change position of the corresponding Tracking Sensor (10 meters away from the previous position). If after all the problem persists, the Tracking Sensor needs to be replaced.