I admit to not being up on the current FAR's re altimeters but is there no
regulation for all aircraft in the US to have accurate altimeters?

I would like to think that mine is accurate within a certain limit since as
this discussion points out it is important. No doubt that in the conditions
that we fly in (changing pressure as the day progresses) there is some
inaccuracy but in my experience not more than a hundred feet or so and as
others have pointed out by tuning in to a local ATIS can be corrected.
Those influences are the same for whatever setting you decide to initially
use anyway.

Casey Lenox
KC
Phoenix