setting ARSPD_ENABLE to 1 and ARSPD_USE to 0 allows the airspeed
sensor to be initialised and logged without it being used for flight
control. This is very useful when initially testing an airspeed sensor
in a new plane. It also makes it possible to enable/disable the use of
the airspeed sensor during a flight at any time.
when MANUAL_LEVEL is set to 1, we don't do accelerometer levelling at
startup, and instead used the values saved in the EEPROM. This makes
it easier to do levelling on the bench, or once for a series of
flights for the day
Amilcar Lucas
Michael Oborne
Andrew Tridgell