In article ,
Ron Natalie wrote:

john smith wrote:

The pilot leans until roughness, then enriches a couple quarter turns.

If he doesn't have an EGT gauge, using roughness or RPM peaking is
not a bad system.

The aviator calculates density altitude and uses the CHT/EGT to
accurately adjust the mixture.

Tell me what possible use a calculated density altitude or CHT is
for setting the mixture. A EGT with reasonable response time is
preferable, other than that using the RPM peaks/roughness is as
as good as can be obtained. I can tell you on my plane, that
even using my multipoint EGT I get mixture settings not substantially
different (save a little better fuel economy) than the "lean to
roughness" technique.

Consider the fact that many pilots do not even look at the tables in the
POH/AOH.

Additionally, they have no clue what the manufacturer recommended
degrees rich/lean of peak to operate at max power or max range.
How much do you adjust the mixture after attaining roughness? A little?
A lot? Just enough to smooth it out? That kind of adjustment can kill an
engine quickly.

Consider the fact that many do not even care!