The one instrument I never trusted much in single engine G/A airplanes was the airspeed indicator. Luckily it usually reads low, not high, if you've got some dirt or a bug in there.

Even if it's clean when you depart, all it takes is one unlucky bug into the pitot tube and it's gone, so you'd better learn how to fly without depending on looking at the airspeed indicator the traffic pattern.

This is why I really liked the "Bacon Saver" AOA vane mounted on the left wing strut. I never had to look inside for airspeed in the pattern.