J. Severyn writes:

It is called the "red fin" in this write-up by Cirrus....same thing.
http://www.cirrus147.com/training/LOPops-3-195278.pdf

OK, I think I've got it. The red box is the area where you heat up
the engine enough to reduce engine life over the long term, without
any clear advantage for fuel consumption or power. If you are leaner
or richer than the box, you get longer life and a better power/fuel
trade-off.

Mxs, maybe we can get you to fly a real aircraft if we keep this up.

That would require lots of time, lots of money, and some other things.

--
Transpose mxsmanic and gmail to reach me by e-mail.