When correcting for east variation in isogonic lines, how is the variation adjusted?

When correcting for east variation in isogonic lines, the correct adjustment involves subtracting the variation. The isogonic lines on a chart represent the lines of equal magnetic variation, which indicate the difference between magnetic north and true north.

When the magnetic variation is to the east, this means that magnetic north is east of true north. To find the true heading from the magnetic heading, you need to account for this east variation. Subtracting the east variation from the magnetic heading gives you the true heading.

For instance, if a pilot has a magnetic heading of 090 degrees and the variation is 5 degrees east, they would subtract 5 from 90, resulting in a true heading of 085 degrees. This practice ensures that the aircraft is navigating correctly relative to true north, thereby maintaining accuracy in navigation and safety in air traffic control operations.