EKF2 IMU voting

#1

I know there are a total of three IMUs in the case of Pixhawk 2.1 Cube.

  1. Which one of these is the 0th accelerometer?

    What is the number of accelerometers that are damped in the Pixhawk 2.1 cube?

  2. What is the logic of choosing the best of the three IMUs?

Or the corresponding source code?

  1. If you are using external GPS, the magnetometer in this GPS seems to be used as the primary, does this magnetometer mean zero magnetometer?