71. Variation
Difference between true north
and magnetic north
North pole and magnetic pole
differ
Annual change
Found on compass rose
Varies globally
72. Compass Rose
004 1/2°W 1985 (8' E)
4.5º West variation in 1985
8’ annual change
Current variation 3ºW
8 X 34/60 = 4.5º change
4.5 – 4.5 = 0
Subtract when annual change
and variation directions differ
Add when same
73. Deviation
Difference between ship’s compass and magnetic
bearing
Ferrous metal affects magnetic field on vessel
Relative to vessel’s heading
Found on deviation card / table
No deviation in hand bearing compass