How to Calculate the Azimuth On a Roof Plan

Stand directly at the bottom of the slope of the side of the roof for which you wish to calculate the azimuth.

Hold the compass level in front of you. The red side of the dial will turn and then stop at True North.

Imagine a straight line running down the slope of the roof and over the compass. Measure the degree of the difference between the imaginary line and the line running through True North. Remember, North is 0/360, East is 90, South is 180 and West is 270

Compensate for magnetic declination, which is the difference between magnetic and True North. A compass measures Magnetic North. To compensate for the difference, find a map of your area online that has a compass printed on it indicating where North and South are located. Print out the map. Lay the map down so that the compass printed on it faces True North. Place the other compass on the map. Measure the degree of difference between True North indicated on the map and Magnetic North indicated by the compass. Subtract the degrees from your azimuth measurement if the compass is to the right of True North. Add the degrees if Magnetic North is to the left of True North.