velasquezrush

It will takea few years to change for more than 1 degree. No argument there. BUT... The concern is that older handheld units have the same old database, and mag north drifts a good bit over time. When trying to project a waypoint for a cache at a considerable distance (and some owners get a kick out of mentioning their use of magnetic in the cache description to fool you instead of true), it can make a large difference to the result if the table is outdated. We have no evidence that even firmware updates also update this table, and some units haven't even had a firmware update in ages.

And we have sometimes the same errors in airplanes ... hahahaha.. but it is not a big deal because we fly a straight magenta line based on Gps coordinates and magnetic track info is shown just to verify that we are flying the same magnetic course shown jn the navigational charts. I want to know if the built in isogonic line database for the etrex 20 could be updated.. did Garmin tell you something about it?

It is a built in isogonic line database. Airliners uses the same principle because, besides the regular backup compass, there are no magnetic navigation instruments in a Boeing737. Magnetic track and heading showed to me is derivated from the True Heading and True Track obtained from the GPS and adjusted by the isogonic lines database.

Etrex 20 shows magnetic heading because it has a built in data base with the magnetic variation on each part of the planet. You will use the feature by just selecting Magnetic aHeading. If you travel to another place with a different magnetic deviation, you will realize that magnetic variation showed by the gps will be different. I am an airline pilot and our navegational systems, Inertial Reference System, uses and internal database to show the pilot the magnetic track based on the true tracked obtained by the aircraft Gps's. Same principle.