How to figure declination, using a GPS

[TerryC]

On ALL topo maps, on the bottom margin, is a declination value for the area on the map. More correctly, for the center of that topo. The declination value is the difference between true north and magnetic north.On the west coast it can be 17 degrees or more. Your life, or safety, may depend someday on knowing how to figure the difference where you are. Today's Navy STILL learns how to use a sextant to backup today's electronic navigation systems, although compass stearage, I believe, has officially been retired. To figure the declination where you are, using only your GPS is easy. Plug in a "go to" formula. Record the "magnetic" value for the "go to" bearing. Then change the "go to" value to the "true" bearing value. The difference is the declination where you are. If you put a piece of masking tape on the back of your unit, you will have a handy place to note the value. If you change your location, change the tape. Lastly, NOTHING replaces the safety and security of knowing how to use the "old fashioned" magnetic compass. TTC

 

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[fatman4570]

In my wornout opinion, anything that runs on power and is used in unfriendly conditions will always fail at the worst possible time. Everyone should know how to use a map and compass. Sometimes your best find will be your vehicle.

 

[goverton]

In my wornout opinion, anything that runs on power and is used in unfriendly conditions will always fail at the worst possible time. Everyone should know how to use a map and compass. Sometimes your best find will be your vehicle.

Question: If I have an old Plat map from the 1870's with declination on it, should I convert that to today's declination on modern map or stay with old declination?

 

[Tom2hunt]

Yes, you should convert it to today's magnetic declination field. The magnetic north is moving westward about 1 degree every 5 years. You can call the FAA tower airport in your closest town that has one and ask "what is the magnetic field for this are". You also might be able to do a search on the internet for an FAA tower in your area to get the magnetic field.
Here is some other readings that will help. http://www.learn-orienteering.org/old.
http://www.ussartf.org/compass_basics.htm.

I have my compass around my neck all the time and I use it.

 

[TerryC]

Yes, you should convert it to today's magnetic declination field. The magnetic north is moving westward about 1 degree every 5 years. You can call the FAA tower airport in your closest town that has one and ask "what is the magnetic field for this are". You also might be able to do a search on the internet for an FAA tower in your area to get the magnetic field.
Here is some other readings that will help. http://www.learn-orienteering.org/old.
http://www.ussartf.org/compass_basics.htm.

I have my compass around my neck all the time and I use it.

I very much agree with you on the latest MN value. In '88, I bought a large sailboat when I lived in Milwaukee, WI, my hometown. Then, the MN 0 degrees went smack-past the harbour entrance. GN and MN were virtually the same. Nice! Now, zero is over in western WI. Even maps of just 20 years ago need to be "buried with honor". TTC