Compass rose:– Every chart has at least one compass rose overprinted on it, and most have three or four. Printed in magenta, most roses have two concentric rings; the outer one shows true directions and the inner shows magnetic directions.
Locate the closest compass rose to your location, and just above its center crosshairs you will fi nd a label noting the local variation (as of the stated year) and its name—east or west.
Just below the crosshairs you will find a note of the annual increase or decrease in variation. Take the difference between the year shown and the current year. Multiply this difference by the minutes of increase or decrease. If increasing, add the difference to variation. If decreasing, subtract the diff erence. Round your answer to the closest whole degree of variation
Sometimes the annual change in variation is noted as east or west, rather than increasing or decreasing. If the annual change has the same name (east or west) as the variation, variation is increasing. If the names are opposite, variation is decreasing.
For example: If your compass rose says 20°20’W (20’E), this indicates a decrease of 20 minutes a year because the names, W and E, are opposite. If it says 20°20’W (20’W), that would indicate an increase by 20 minutes a year because the names are the same.