The generic answer is: Fancy math
The Dynon EFIS units use airspeed as an assist to figure out what level is. All EFIS units in our price range (and up to about 10X our price range) use inexpensive gyros that drift over time. You have to use some external information to help correct this. We use airspeed.
When you give the unit airspeed on the ground, here's what the unit thinks:
1) I just accelerated from 0 to 150 knots in .8 seconds. Who put me in a top fuel dragster?
2) The gravity vector didn't move at all. It's still 1 G straight down, with no forward, back, or side-side component.
3) The only way 1&2 could be true at the same time is if the airplane followed a perfect ballistic path where gravity cancels out all other accelerations.
4) But you accelerated too fast (about 6G's), so this is impossible, so something is up, so it's time to rethink all of this and say "horizon recovering" until we're sure.
If you give it airspeed slower, it won't grey out, but it will still show the pitch down.
P.S. If your airplane actually can accelerate from 0-150 knots in less than a second, can I have a ride please?
