"G.R. Patterson III" wrote in message
...
How about one electric AI and one vacuum AI? That is the best of both
worlds.

Which one do you believe when they don't agree?

One hopes that a look at the vacuum gauge and the ammeter would help you
with that. Of course, if the instrument itself has failed, you have to fall
back on the traditional cross-check techniques, but that would be a
possibility anyway. Besides, it's much more common for the power source
(vacuum or electric) to fail than for the instrument itself to.

Pete