Using the LAMS rule, what operation is used to obtain the back azimuth from a forward azimuth of 250°?

Using the LAMS rule, what operation is used to obtain the back azimuth from a forward azimuth of 250°?

• A. Add 180
• B. Subtract 180
• C. Ignore and reverse direction
• D. Double it

Answer: (B)

When you need the back azimuth, you’re looking for the direction directly opposite the forward azimuth. In a 0–360° system, opposite directions differ by 180°. Using the LAMS approach here, you subtract 180° from the forward azimuth. So with a forward azimuth of 250°, subtracting gives 250° − 180° = 70°. That 70° is the back azimuth, pointing directly opposite along the same line. If a subtraction ever produced a negative value, you’d add 360° to wrap around, but in this case it stays within the 0–360° range.

When you need the back azimuth, you’re looking for the direction directly opposite the forward azimuth. In a 0–360° system, opposite directions differ by 180°. Using the LAMS approach here, you subtract 180° from the forward azimuth. So with a forward azimuth of 250°, subtracting gives 250° − 180° = 70°. That 70° is the back azimuth, pointing directly opposite along the same line. If a subtraction ever produced a negative value, you’d add 360° to wrap around, but in this case it stays within the 0–360° range.