Altimeter Calibration Height

"Neil Gould" wrote:
The original question asked whether the altimeter is set to indicate
the altitude at the wheels or "at the level...",
and if that question has been definitively answered, I missed it.

Assuming an aircraft of large vertical dimension...

If the point of an altimeter is to directly display to the pilot how far
the lowest point on the aircraft is above surface obstructions (or wheels
above a runway), then I would presume the altimeter would be calibrated so
that when the aircraft rests on the ground it reads the same altitude as
that ground level.

If the point of an altimeter is to directly display to the pilot the
altitude to fly so that the aircraft is as far as possible from other
aircraft also obeying 91.159, then I would presume the altimeter would be
calibrated so that when the aircraft rests on the ground it reads the same
altitude as the ground level plus half the height of the aircraft.

And so on for other uses (e.g. keeping the distance of the top of aircraft
safely below a cloud ceiling of known altitude).