There seems to be a distinct lack of the KISS principle at play... I have had the Airspeed on an EFIS go screwy. Seeing I wasn't smart enough to analyse all the permutations and combinations of what the computer may or may not be doing, I held a straight and level attitude on the AH and checked I had cruise power set (as per my initial IFR training in a rickety old Seminole) Seemed to work out ok...