I'm looking for a good, no-nonsense explanation of the variation of
pressure with altitude.

Google reveals many, many pages, most of which are either over
simplified (altitude decreases pressure) or way to complicated;
plus, most of the ones that actually present equations are aimed
at altitude variations in the thousands or tens of thousands of feet,
while I am concerned about hundreds.

Basically what I want to know is this:  can I use a pressure
sensor with an absolute range of up to 30 PSI to measure within
10 to 20 feet the difference in altitude between the current position
of a sensor package and the position at which the package was
initialized?  At altitudes of 1000 feet or less?

Please pardon the bass-ackwards US measurements, but
pressure is one of the few things I don't have a good feel for in
metric (distance, mass, speed, volume, and especially time
aren't so bad ;-) ).

I have also found pages with pressure based altimeters for model
aircraft and rockets, but they tend to be sketchy on the details
and I really want to understand this, rather than just having an
answer for how to do it handed to me.  I find understanding to be
far more valuable in the long run.

Mike H.
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