ALTITUDE & PRESSURE... Computes
the relationship between pressure and altitude, based on standard meteorological
data (Smithsonian Meteorological Tables). This does not adjust for any effects of weather
on local pressure.
Note that due to rounding errors, the calculations are not 100% reversible (e.g. computing the pressure at a given altitude and then using that computed pressure to calculate altitude will not yield the identical initial altitude  but it will be very close).
