My older Magellan GPS give me a choice of magnetic or true North. Does yours? Which one do you use and why? I'm not sure what the difference is.

 

I always use True North. That never varies. Magnetic North Is actually 950 Kms away from True North and the Magnetic Declination (difference between True and Magnetic) is not the same for any two points on the earth. The farther north you go the larger the difference. Not to mention the fact that Magnetic North moves, slowly but does move. For example, when Lewis and Clark were trapsing through the northwest the magnetic declination was about 6-7 degrees. Now in the same area it is about 14 degrees.

There's a good web site at http://tinyurl.com/czmzq that does a good job of explaining this.
Bob

 

I'm going to suggest using a magnetic setting for your GPS for this reason; It will simplify navigation between the GPS and the compass that reads magnetic. (always carry a compass).
And keep in mind that considering the GPS is an older model, it probably does not have an electronic compass......which means that the compass in your GPS is only reliable when the unit is moving......at greater than walking speed.
The one nice function you do have in regard to your GPS compass is that when referencing a waypoint, the "bearing"........the direction to the waypoint in the digital mode......is accurate whether or not you're moving.
It's true that declination changes over time......and is most dramatic as you change longtitude.....it is so slight as to be a non-issue if your not moving across the country. (you can determine the declination in your area by going to the USGS site)
Remember most maps are layed out based on true north. When using your magnetic compass to orient the map, align the map to magnetic north, then move it the xx degrees to true north.....xx being the declination for that area.
It's a really simple method to use......and please remember that GPS, map and compass always go together.

 

OK, I'm gonna agree and disagree with the previous posts. I agree fully that a compass should be carried to back up a GPS unit and that an accurate map of the area being traversed should be carried.

If at all possible use a map that has a compass rose on it. This is an area on the map printed to show the magnetic declination for the area and is very helpfull when planning a route to follow. If such a map is not available check with the local road department and they will be able to give you an accurate declination reading.

Also be aware of the effect that underground deposits can have on a compass. It is a good idea to check you compass against the sun with your watch when you are able to see the sun. (For those that don't know the trick, point the hour hand at the sun, halfway between the hour hand and the short way to 12:00 O'Clock is South. Don't forget to correct for daylight savings time if it is in effect.)

I prefer to use True North when navigating as that is the way I learned. I put a small dot of paint on the edge of my compasses at the declination for our area and keep an eye on my backtrail so I know what to look for on the way back out.

 

Something that you must keep in mind when refering to declinations provided on a map...... they are based on the datum.....and the datum will often be NAD of 1927 (North American Datum) This is the model the map is based on. If this is the case, your declination info is 78 years old.
This doesn't necessarily degrade the accuracy of the map......just the applied declination.
Often, the map will be a NAD 83 or USGS of 1984. All of this info is most often found on the bottom right or left of the map.
Now the critical point......(I know this is a bit of overload, but important).....the datum in your GPS MUST be the same as the referenced map, or your location can be off by as much as 200 meters. In heavy canopy, this can be a problem.
Your GPS has many datums available in its menu.....just check in your map setup.
If you are transmitting your location to someone else with GPS, make sure you are both on the same datum.
If you are entering a location into your GPS from a map, make sure the GPS is set to the same datum as the map BEFORE you make the entry. Changing the datum after the entry will NOT work and can lead to navigational errors......in some cases, miles.
I know this is a bit more info than you wanted, but these are critical points when using a GPS and ending up with satisfactory results.

 

Thank you all. These are all good points. Because I navigate mostly by compass while on my boat, it makes best sense for me to continue to use my GPS in the magnetic North setting. It made more sense after reading these posts. As far as the datum goes, I appreciate the info. I know the GPS has the settings and did not know how to use them. Now I do.

My next GPS questions for you gurus. My older Magellan does not work well or at all when it's heavy fog or overcast. Do the newer models and brands work better now or am I just as well off keeping my older unit?

 

fish........overcast or fog should have little or no effect on your GPS reception.........what I'd want to know is if your unit is a parallel channel (all units now made are) or is it the old "multiplex" type.
If it is a multiplex unit, I'll stop here and recommend you look at updating to the newer parallel channel GPS.
A multiplex unit reads one satellite at a time and will tend to loose signal very easily..........this may be what is happening.
The following are a couple of excellent reference books; GPS Land Navigation by Michael Ferguson, The GPS Handbook by Egbert and King.
GPS is a great tool........and they are only going to get better, but a through basic understanding is the the key.........and a must.