Encouraged by help from several here I decided to do a repeated autotune - to see if I would achieve improvements on subsequent autotunes.
I neglected to consider the impact of battery charge state.
While I was pleased that I was able to complete two 3-axis autotunes on a single charge, I have the feeling that the second autotune is ineffective as it started with the battery on about a 75% charge.
Below are the mavlink messages with the autotune results. Does this suggest that my hunch is correct - and that I should do repeat autotunes all on fresh batteries?