Ardupilot is using a range of sensors and GPS data to calculate the vehicle position, attitude and other data (e.g velocity). The onboard processor runs several algorithms that can provide this data. The outcome of each process can be logged in different messages.

The sensors (gyros, accelerometers, magetometer) are usually grouped in the units called Inertial Measurements Unit (IMU). While most of the hardware that we use have one IMU (IMU0) some of the units may have two of them (additional IMU1).

In vast majority of cases, the results from each process and each IMU are identical. In some rare cases, especially when the sensors are of less than average quality or the environment is challenging (vibrations, low GPS signal, etc) some of the processes will work better than others and will provide smooth and quality data while others may have gaps.

Until recently FlightCoach was able to display one of the sources of data and for one IMU only. We have now enabled the user to select other sources for up to two IMUs. This selection may make a difference for diagnostic purposes or a recovery of individual problematic flights with small gaps. For vast majority of applications, the selection of the source should not make any noticeable difference.

POS/ATT/XKF1 – this is a new source that has been recommended by Ardupilot team as the most stable and reliable. It has been set as a default.
XKF1 – this has been the FlightCoach default source of data until now.
POS/ATT – this is source does not require running Kalman filter EKF3. At this stage it does not provide velocity information but we might extended it with the GPS velocity data.
POS/XKF1 – this is source is a mix of the first two options.

IMU0 – default IMU.
IMU1 – secondary IMU.