Thanks for the replies. I have turned it off and gone from there but am still interested as to WHY it would be recommended to run more than one compass.
Apart from the APM start up "sanity check" is there any further cross checking of compasses during flight?? If too far out, do they trigger a failsafe?? Do they back each other up - ie if the primary fails during navigation does the Pixhawk switch to the secondary??
In addition under what circumstances would you run 3 compasses (as this is provided for on the compass screen)
Thanks for the thoughts