Small Nav Q
 

I keep getting (A). The answer is (B) apparantly. Could someone put me out of my misery. Many thanks in advance.

Given:
True track 180°
Drift 8°R
Compass heading 195°
Deviation -2°
Calculate the variation.
A 21°W
B 25°W
C 5°W
D 9°W

I think the answer is 5w.

C D M V T
195
-8
187 -2 185 5w 180

Does this ring any bells ?

True head = 172
Compass = 195
Dev = 2W
Magnetic Head = 193
Therefore Var = 21

Where am I going wrong?

I'm not a small nav (I can think of many who are) but I'll answer your question anyway.

You are right. The answer is (A). The person who tells you that it is (B) has not applied deviation correctly.

When deviation is given as plus or minus, it is what you apply to the compass to get magnetic heading, not the other way round. So plus is East deviation and minus is West deviation. The magnetic heading is 193.

well done Cron. You were right.
I can see that I should have taken the drift from the true Hdg rather than from compass Hdg.

Thanks for your input oxfordblue.

I came up with (a) as well. The mnemonic for that is Cadburys Dairy Milk Very Tasty.
Compass Hdg 195
Drift 8R
Compass Track 203
Deviation -2, so
Compass Track 201 Magnetic

If this is equal to a True Track of 180 True
The variation= -21

Remember to apply the Cadburys Dairy Milk Very Tasty from left to right as you read it- C>D>M>V>T and memorise:

Variation West, Magnetic Best
Variation East, Magnetic Least
(applies for Deviation too)

(does anyone know what I'm talking about?). That was quite an exercise for my brain cells after all these years! Have I made a boob above?

The book I learned from: Can Dead Man Vote Twice? Wicked question, so to speak.. ;) For me, the math ends up the very same as stated above. ....

FD.

The answer is B

If your true track is 180 with 8r drift you are actually heading 172 (As you are being pushed 8 degrees to the right)
If your compass heading is 195 with a -2 degree deviation your actual magnetic heading is 197 (As your compass is reading 2 degrees less than the actual magnetic value)
197 minus 172 is 25 degrees so the answer is B.

Regards
EddieHeli

My money is still with Oxford Blue answer (A) 21w.

Deviation west compass best.
Deviation east compass least

Minus = west
plus = east

Now I am going to dig out those old Nav books...

Sorry EddieHeli, you've applied deviation incorrectly as well. Oxford Blue is right, it's answer (A).

The problem with using + and - for deviation and variation is that it only works mathematically correctly when working in one direction. For instance:

Compass heading 182º, Deviation -2º, Magnetic heading 180º

is correct and makes sense mathematically because 182 - 2 = 180 whereas:

Magnetic heading 180º, Deviation -2º, Compass heading 182º

is also correct but makes no mathematical sense. I would suggest a variation of Notso's idea. Convert the minus sign to 'west' then say:

Deviation West Compass Best
Deviation East Compass Least

Where 'best' means 'a bigger number'. Variation is similar, + is east, - is west as before. The rhyme is as Notso says:

Variation West Magnetic Best
Variation East Magnetic Least

Alex, brilliant- I knew there was more to the poem! Who says pilots can't be poets as well! Maybe the poetry is a bit dry, but it's functional! Bit more handy than that:
"I wondered lonely as a cloud
That floats on high o'er vales and hills......"
Really, what use is that rubbish to a mechanic or engineer?

I tried to make it clear:

Good question Cron, got any more questions to practice on??

G-ANDY

G-Andy, yes, I have a few more in this vain, if they are useful to folks practising. The problem is they are gleaned, filched, copied from all sorts of places and may be copyright. Does this apply to questions? If not I'll post some up. Alex?

More poems
 

Can Dead Men Vote Twice At Elections

Compass Deviation Magnetic Variation True Add East

I prefer CDMVT but the other way round is,

True Virgins Make Dull Company Add Wiskey

True Variation Magnetic Deviation Compass Add West.

Hope that helps.

Unowho

I disagree,

I think it depends how you read the question.

The deviation is given as -2 degrees. I read this to mean that your compass is underreading by 2 degrees, therefore a reading of 195 is actually 197.

I therefore stand by my answer.

why do you say Convert the minus sign to 'west'

surely East is Least, West is Best

therefore East is minus West is plus


Regards
EddieHeli

EddieHeli, the problem with the rhyme 'east is least, west is best' is that it doesn't tell you what is best. The conversion of + to E, - to W is just a convention, its just so everybody understands it the same way.

Does "Meridien east, Greenwich least" help things at all? !!!;)

+ or - Deviation
 

E H. Alex is RIGHT you are WRONG

Quotes

"The angle between Magnetic North and the direction indicated by a compass needle is called the angle of DEVIATION"

"Deviation is the angle between Magnetic North and Compass North measured in degrees East or West FROM Magnetic North"

"The signs for plus and minus are sometimes used as a prefix instead of the suffixes East or West, in which case you will see that the rule to apply the deviation (as stated) to the compass heading to obtain the Magnetic headin"

Compass 195º Deviation -2º = Magnetic 193º

Hope that clears things up.

EH is it different in helios????????????????

Unowho

unowho

I disagree and stand by my answer.

To use your quotes

"The angle between Magnetic North and the direction indicated by a compass needle is called the angle of DEVIATION"

If you have a deviation of -2 degrees then you must add 2 degrees to your compass heading to get magnetic north.

To visualise this draw a line straight up and call this magnetic north.
now draw a line 2 degrees to the left of it (i.e. to the West as everyone is saying minus is to the West).

using your own quote
"Deviation is the angle between Magnetic North and Compass North measured in degrees East or West FROM Magnetic North"

Although my compass heading is now saying north It is actually pointing 2 degrees to the west of north.
Therefore I must add these 2 degrees on to my compass heading
to get true magnetic.

so 195 compass heading must have 2 degrees added to give true magnetic therefore 197 is the answer.

The answer is in your own quote "FROM Magnetic North"

Yours and everyone elses answers are going FROM COMPASS NORTH.

You are all saying that magnetic north is 2 degrees to the west of your compass North.

If you take the two degrees off you are then out by 4 degrees.

<<Although my compass heading is now saying north It is actually pointing 2 degrees to the west of north.
Therefore I must add these 2 degrees on to my compass heading
to get true magnetic.>>

No, if your compass reads North and it is pointing to the west of mag N. then you must takeaway 2 degrees to get mag hdg!

If CompNorth datum is to the left of MagNorth datum by 2 degrees, you use up 2 degrees of your Compheading before you reach the zero of Mag North.