How to Determine Local Variation
While standing the QMOW, you will routinely be tasked with
determining variation. This is a simple procedure using simple
mathematics and the charts compass rose. Use the following steps to
find your local variation.
Locate the compass rose nearest to the area in which the ship is operating.
Locate the variation and annual increase/decrease from the center.
Locate the year from the center of the compass rose.
Subtract the year indicated from the current year.
Multiply the number of years times the annual change.
Add the sum (or subtract if decreasing) from step No. 5 to the variation in the
center of the compass rose.
Round the total off to the closest ½°.
Figure 2-5. Steps followed to determine variation.