- Board question
How do you determine a back azimuth?
If the azimuth is less than 180 degrees, add 180 degrees. If it is 180 degrees or more, subtract 180 degrees. In mils, add or subtract 3,200.
- TC 3-25.26Publication
Map Reading and Land Navigation
TC 3-25.26 is the Army's map reading and land navigation manual: grids, marginal information, terrain features, azimuths, and navigation techniques. Dated November 2013, it is still the active reference used on land navigation courses and at boards. Note the designator -- it is a TC, not an FM or ATP.
- Board question
What is the G-M angle?
The grid-magnetic angle: the angular difference between grid north and magnetic north for that map sheet. It is shown in the declination diagram along with the conversion instructions used to change a magnetic azimuth to a grid azimuth or the reverse. Always use the conversion notes printed on the sheet you are working from.