I did some more research and found interesting tidbits about altimeter
calibrations. References at end.

Thanks Kev. Very interseting.

The answer can be taken as: the
height of its installation... as referenced to a
standard datum of 10' above the wheels.

I'm not sure what this means. No surprise, it was probably written by a
government lawyer. However, at least wheel height is being taken into
consideration. Somehow. Maybe it means the altimeter is supposed to
read ten feet low, to account for the wheels.

[cat II] "Two sensitive altimeters adjustable for barometric
pressure, having markings at 20-foot intervals and each having a
placarded correction for altimeter scale error and for the wheel
height of the aircraft."

From this I glean the altimeter should read its own height, and the
altimeter's height above the wheels (on flare? on the ground?) must be
available to the pilot. Further:

For instance, a large aircraft which has a
19-foot wheel-to-instrument height would require
a nine-foot correction under this rule.

I infer from this that the first ten feet require no correction, and
thus I infer that the altimeter indeed should =indicate= ten feet lower
than its own height, even as it =senses= the =pressure= =at= it's own
height.

Jose
--
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