>On can always go GPS, get a fix on at least four sats and
>the GPS spits out current altitude, quite accurate AFAIK. TTYL

Not according to what I have read. It can be up to 50 feet out, and it is
because of the way it is calculated. This is borne out by personal
observation of having just got a GPS receiver and "finding where I live" and
comparing it to a survey map.

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