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Recently there was some discussion here about the observed angles on the datasheets and how to work with them. Having been in the mil. and only dealing with grid and mag azimuths the use of true north was never really gotten in to. I have tried to find on-line mind you more explanation in regards to this and im still say confused. What i would like is someone in the know to use as an example say EB2570 (current) and figure that and tell me how you came about your answer. Or take me to an online source that explains it better than what i've gotten so far. Oh and the declination for EB2570 is -8 degrees or 8 west. Anybody thanks alot for your time.

Edited by a/r/sf/ret
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A map of US magnetic declination can be found: Webpage Fortunately right now St. Louis is near 0deg. declination so I just ignore it. Magnetic North here is almost the same as True North. However it will different in different places (and at different times).

Another place to look would be:

Webpagewhere I think that you could get the declination for a particular spot and time.

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Okay, getting the declination for a spot is no problem....its using that to convert the true north headings used in the datasheets as "observed angles" to magnetic for use with the compass thats confusing to me. Thanks

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Remember this: “Declination West, Turn Azimuth Ring West!”

When going from MAP to TERRAIN --> ADD (CCW).

When going from TERRAIN to MAP --> SUBTRACT (CW).

For example, if your declination is a negative value (meaning West), and you're converting from True North to Magnetic North, you ADD the declination to the bearing (turn your compass ring counter-clockwise).

Here in northeast PA my magnetic declination is roughly -12½°. If, for example, the True North bearing I get from the box score on the datasheet says 142°, I set the azimuth ring on my compass to 142, then continue to turn it counter-clockwise to 154½. Do the reverse if you take a compass bearing and want to know what the True North value is.

I made a little cheater card that I keep with my compass 'cuz I always get the directions confused no matter how many times I have to apply them! Hope this helps.

Cheers ...

[Edit for typo.]

Edited by Rich in NEPA
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For EB2570, just add 8 degrees to get the Magnetic Bearing.

PID.......Reference Object..........Distance..........Geod. Az

......................................................................dddmm

EB3512 PHILADELPHUS RM 1.....32.740 METERS 06055

EB3513 PHILADELPHUS RM 2.....35.966 METERS 32201

To locate the Reference Marks from the Station Mark:

Bearing to RM1 is 60 deg 55 min ~ 61degrees True

Bearing to RM2 is 322 deg 01 min ~322 degrees True

Bearing to RM1 is 61 + 8 = ~69 degrees Magnetic

Bearing to RM2 is 322 + 8 =~330 degrees Magnetic

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Thanks Rich and Terra very much I believe I have the problem solved now with your help and examples. Notes made. Particular example has no refs. left but a measurement from a road. Found all the rest cept-in the Az Mk which was destroyed years ago. Gonna get that RM mark though.....thanks again

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