Navigation - How to adjust a Magnetic Compass for Declination - Pt 1

This is a short video that explains how to adjust a magnetic compass for western declination.

[PhilipTaramai]

Thank you for making it simple ... all other videos confused the heck out of me.

[TyJee]

The A - 30 compass (and most other base plate compasses) has a built in fixed mag, declination scale that makes adjusting for mag. declination very easy. Another easy way to adjust for mag. declination, and get the compass direction of travel arrow pointing to the correct bearing -- is to use that fixed mag. declination scale printed inside the compass capsule. It does the same thing as shown in the video. Only a little bit different process.


Set the N on the bezel ring to the index line. Turn the compass to "box the needle". Then, following your example in the video of 20˚ West mag, declination. Turn/rotate the compass base CW until the compass needle is pointing at 20˚ on the West Declination scale. Hold the compass base stationary while you turn the compass bezel CCW to move the N to the tip of the compass needle. Do the same thing, but in the opposite direction for East mag. declination.



[[ You can also use the fixed mag scale to do the same thing when taking a compass magnetic bearing back to the map, to get the correct bearing to use on the map, and avoid doing any math to account for mag. declination. ]]


For example: If you measure a bearing to a cell phone tower with your compass of 45˚ [the compass needle will be boxed inside the orienting arrow] If the local mag. declination is 10˚ East. Just hold the hold the compass base stationary, while you turn the compass bezel CCW so the that compass needle is pointing at 10˚ East on the fixed mag. declination scale printed inside the compass capsule. You will see that the bearing at the index line of the compass has changed from 45˚ to 55˚. [ 45˚mag bearing + 10˚ East mag. declination] .. 55˚ will be the correct bearing to use on the map. Easy, No math method.



I like to use an acronym and associated phrase of my own creation. An alternative to the L.A.R.S. acronym.
Maybe others will like it, too. However, maybe I remember it more reliably because I thought it up myself.

[[ WAvES - West Add v East Subtract. ]] ( the "v" symbolizes the mag declination diagram arrows). And of course WAvES is from thinking " magnetic waves."
With the phrase:

[[ The Map WAvES to the Compass, and the Compass WAvES back(ward) to the Map. ]]

Meaning a 50˚ bearing measured on the map, for a West mag. declination of 20˚ you would add 20˚ + 50˚, and set the compass to 70˚. But when taking a compass magnetic bearing back to map, you do the math back(wards). West Add becomes West Subtract. If the compass magnetic bearing = 230˚, and mag declination is 20˚West, on the map you would use a bearing of 210˚ [230˚ - 20˚].

In the same way for an East mag. declination of 10˚ East. "the Map WAvES to the Compass. A 30˚ map bearing becomes 20˚ on the compass [30˚ - 10˚]. Or if taking a compass measured magnetic bearing of 45˚ to the map. Then 'the Compass WAvES back(ward) to the Map'. East Subtract becomes East Add. On the map you would use a bearing of 55˚, [45˚ + 10˚]

[kc]

If you are shooting a bearing say a tree is 20 degrees, my area is 11.72e, would my true heading be 8 degrees, do I set the compass to that? Or follow the magnetic bearing ?

Hope it makes sense as Im trying to understand taking a bearing off the land and not the map

[bowieknife]

Hi thanks for your video... What does a declination of 3°2' west mean? Three point two degrees?

[robonkenhout]

Good explanation. Sometimes less information is better.

[kevin]

Question - So after you set the compass to true north. I just need to align the needle with the 20 (after you moved the bezel) and I will be going true north? (using your example of how many degrees I need to adjust)

[jamesashford]

Everything on maps are based off True North because True North always remains the same fixed point. Magnetic declination is a fluctuation over a few hundred miles over a few decades. In other words whatever your magnetic declination is now at your current location, it will slightly adjust differently within the next 10 years or so even though you are at the same place. Magnetic North always fluctuates and that is why maps are drawn according to true North.