Declination, Magnetic Bearing and True Bearings

I am really confused for how to convert back and forth in between these three, declination, magnetic bearings and true bearings.. In Reza's book, Chapter 3, problem # 11, gives the formula: True Bearing = Magnetic Bearing minus Declination..

If I look now at the Cuomo book, Example 4.5, it is done as True Bearing = Magnetic Bearing plus Declination..

I am confused which is it.. and if someone has quick notes on how would you go from one to the other.... I get confused also in the directions, E or W.

Thanks..

passpepasspe said:

I am really confused for how to convert back and forth in between these three, declination, magnetic bearings and true bearings.. In Reza's book, Chapter 3, problem # 11, gives the formula: True Bearing = Magnetic Bearing minus Declination..
If I look now at the Cuomo book, Example 4.5, it is done as True Bearing = Magnetic Bearing plus Declination..

I am confused which is it.. and if someone has quick notes on how would you go from one to the other.... I get confused also in the directions, E or W.

Thanks..

Click to expand...

Don't memorize formula. Think it in a logical fashion. First, draw/plot magnetic north. If magnetic declination is given, say 10 degree west, then the magnetic north will be 10 degree west to the true north. Now, if magnetic bearing is given, say North 50 degree west, then from the previously calculated or drawn magnetic north go 50 degree further west. This will be your magnetic bearing. Next, to find true bearing, calculate or find the angle between true north and magnetic bearing, which in this case will be 10 degree plus 50 degree to the west of magnetic north. So it will be north 60 degree west.

Take another example, a magnetic bearing of south 55 degree east is provided and the declination is given as 15 degree east and you are asked to find true bearing. First draw the magnetic north by going 15 degree east of true north. then project is straight down to have magnetic south. From the magnetic south go 55 degree east to have your magnetic bearing of

south 55 degree east. Now, in order to find true bearing, you have to see the direction of true south, which in this case is 15 degree east. So, now subtract 15 degree from 55 degree. So, the true bearing will be south 40 degree east.

I view this type of problem as looking at the card on a ship's compass. True north is fixed at the top of the compass. The magnetic declination and the magnetic bearing are marked on the rotating compass card. If the declination mark was rotated to true north, the bearing mark would be on the true bearing.