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Angle of declination


Jamin

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Hello Jamin-

Here is a longer answer to your question "What is the angle of declination on Hood".

 

Magnetic Declination is the angle, east or west, to correct a magnetic compass bearing to match a printed map such as the standard USGS Quad map (for Mt Hood). Quads are printed with True (or geographic) lines.

 

If you are not using a map to obtain you bearings, but just taking visual bearings on a clear day with your compass from say, Illumination Rock to the parking lot at the Timberline Lodge, you do not need to correct for magnetic declination. You can use the magnetic bearing to return down the hill.

 

You must adjust your compass for magnetic declination if your are taking the bearing angle of a line say from Illumination Rock to the center of the Lodge parking lot from the quad map.

 

Each degree of error will be about 94 feet in a mile. Ten degrees off will be 940 feet. Seventeen degrees off will be 1, 598 feet off from the True Bearing in one mile!

 

Your GPS is set by default to magnetic bearings. If you are using your (default) GPS to give you a compass bearing angle from Illumination Rock to your GPS Waypoint (set at your rig in the middle of the Lodge parking lot) you must not use the True bearing on your compass. Use the Magnetic Bearing.

 

To change your GPS to True, go to set-up, north reference and select True. Note the declination that is reported on your GPS when it is set to Magnetic North. You will find it to be 17 degrees as noted by pindude.

 

The recommended way to handle Magnetic Declination is 1. set your GPS to True North and 2. set your compass to True North and 3. use the USGS Quad Map for your climb.

 

To set your compass to True North to match your map and GPS, use the brass micrometer screw on the correct kind of compass.

 

Purchase a $30 Suunto M3D base plate compass, a $100 Garmin eTrex GPS and a $6 GPS.

 

The total cost to these three functional tools is about $136. You will need to learn how to use them together from reading Freedom of the Hills or taking a Mazama, the Mountaineers or similar class.

 

Google the three words map compass GPS and click on the second listed six page PDF Handout to learn more about backcountry navigation on the web.

 

Have I made any errors? Never trust one person in your group with sole responsibility for backcountry navigation!

--trad_guy

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Hello SnailEye-

Ooops, wrong information. USGS Quad maps (there are over 1,900 in Oregon) are reworked very infrequently. Soon the printed Quads will be phased out and your will be able to get the latest version printed, say from Bend Map and Blueprint in our town.

 

Quad maps print the declination at the time of print release. (This might be 1965). In the fine print the map will note that the declination gets smaller at the rate of one degree every twelve years in the area of Mt. Hood. pindude made a note of this annual change in his post above.

 

Just Google the three words: map compass GPS and read the .pdf document. Tip: do not use quotes when you enter the three word search above.

--trad_guy

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I was using the topo program available here on campus, and it doesn't have the angle of declination marked on it. Unfortunately, my compass cannot be set to true north, but I have been using a compass without that feature for years so that doesn't bother me too much.

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Jamin-

The map programs will give you True bearings from a point to a point using the distance tool.

 

You can put a piece of tape on the clear bottom of the bezel of your compass to mark a new "arrow shed". It is called the Tape Arrow Method. The idea is to eliminate mental math when you are under stress, trying to add (or is it subtract) the 17 degrees to make it work with your map.

 

If you do not have a base plate compass, you might find it good to upgrade. Just Google: best compass for mountaineering. (No quotes.)

 

Good Climbing!

--trad_guy

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Hey blueserac-

The computer map programs that Jamin is using do not provide the magnetic declination information. Your printed ocean charts do provide the magnetic declination and the annual adjustment too.

 

Again, the printed USGS maps do provide this information, but the good computer programs such as MapTech's Terrain Navigator and National Geographic's Topo do not.

 

Just Google the two words - magnetic declination - and put in your location to get the information and an explanation.

--trad_guy

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