nav question - applying variation and deviation
I have a question on how to apply the correction for variation and deviation.
I understand when given the variation, how to work out the Magnetic course, and also when given the Deviation in terms of a degree figure on a given heading, but give me a question where they only provide the compass deviation card, I can’t see how you work out what figure to use for deviation. For example. (Turneth to page 449 of the Thom Nav book if you’ve got it):
For Steer HDG(T) Varn HDG(M) HDG(C)
N(360) 003 012T 8W 020M ?
Now I work this out to be,
True 12 + 8W Varn = 20M as shown.
Then it loows like the deviation is 3E, East least => 20 – 3 = 17C
The answer is 22 in the book. I can’t see how 22 is the answer from any permutation of these figures.
Can anyone explain this?
Help appreciated as it’s very frustrating. The Thom book is usually pretty clear.
Thanks.