[OSM-newbies] Garmin eTrex 20/30 - is altimeter important for recording GPS data for mapping?

[SomeoneElse]

Bill Ricker wrote:
> all barometric altimeters must be calibrated to known altitude or
> known sealevel pressure frequently for any absolute accuracy.
>

... and (at least with my eTrex Vista) the compass needs recalibrating 
by turning it around twice after a battery change.

Cheers,
Andy