[quote=”sweikert925″]But that was before I found that altimeters are really just barometers and that they work by measuring barometric pressure, not actual height above sea level. Barometric pressure changes the higher up you go. But since barometric pressure ALSO keeps changing with the weather, how DO you get an accurate reading of altitude?[/quote]
Since no one answered this part of your question, I’ll chime in.
Aviation altimeters have a current barometric pressure setting window and adjustment knob. You set the current pressure in the window and the displayed altitude is corrected to reference MSL (Mean Sea Level). This is kind of important when flying…
And as for the accuracy of GPS altitude measurements, this comes from Garmin:
[quote]The main source of error has to do with the arrangement of the satellite configurations during fix determinations. The earth blocks out satellites needed to get a good quality vertical measurement. Once the vertical datum is taken into account, the accuracy permitted by geometry considerations remains less than that of horizontal positions. It is not uncommon for satellite heights to be off from map elevations by [b]+/- 400 ft[/b].[/quote]
