Heading capability of e-compass used affects flying performance of a drone system. By reading output data of magnetometer inside drone system in different level of throttle or rpm of blade motor, we can evaluate how robust is the heading capability of the magnetometer.
This diagram shows output of magnetometer is basically intact on different level of throttle (yellow line) when drone is fixed on a static position. This phenomenon is outcome of a robust magnetometer design.
While this case shows output of magnetometer is impacted by change of throttle level(blue line in bottom diagram) when drone is fixed on a static position. Reading of magnetometer cannot even back to initial value when throttle is released. There are faults exists in the design/application of the magnetometer cause this kind of failure.