I don’t mind a bit of fuzz on the airspeed line. IMHO, the thing to watch for are the big spikes up and/or down. Most of the time, I don’t think a single sample matters that much…but if you get several samples that tell the FC you’re at a different speed, it could be bad.
If you get low readings and are flying close, you can hear the plane speed up. The real scary behavior is that Arduplane will sometimes attempt to dive to get above stall speed.
If you get high readings, the software will slow down. A few samples won’t let it get that slow, but there is a stall risk.
My crash on Sunday appears to be caused by this. I calibrated and removed the cover, but never checked the air speed…which was steady at ~16 m/s (about 60 km/h). Nice and stable and dead wrong!
When I did the auto takeoff, the throttle went full for about 1/2 second and then was reduced during the next 2-3 seconds to about 50%. The auto takeoff was set to climb at 20%. This led to a ugly stall.
The previous flight, where I foolishly left the pitot cover in place went fine (I realized my mistake only a few seconds after takeoff and flew in FBWA rather than auto after that point).