TVMDC – Practice – Correcting and un-correcting the compass

In today’s increasing use of electronic navigation aids, the ability to correct and un-correct a compass heading or bearing seems to becoming a lost art outside of a classroom. Here are a few TVMDC Practice Problems to help keep your navigation skills sharp.

“Correcting” is converting a magnetic (M) direction to true (T). “Un-correcting” is converting from true to a magnetic direction. “True” direction is relative to true north (north pole).

Deviation is the failure of the compass to point to magnetic north. Deviation is caused by local magnetic fields on the boat. These fields may be caused by the engine, instruments or other electronic equipment, power wiring, tools or any other magnetic objects. Deviation is specific to an individual boat. Deviation changes with the boats heading. Deviation is read from the Deviation Table on the boat.

Variation is the failure of the compass to point to true north. Variation is read from the compass rose on the chart. Variation is the same for all boats in the same area. Variation is the same for all directions in the same area.

I always use the same order for the formula working the solution either up or down, this always puts the same information in the same order, this makes checking the work easier and makes is easy for someone to double check the calculations. DON’T ever just do the good old piece of scratch paper where you just add one number to another, that seems to produce much higher rates of errors.

              ↓         T      ↑                True
     (-) E    ↓         V      ↑     (-) W	Variation
              ↓         M      ↑     	        Magnetic
     (+) W    ↓         D      ↑     (+) E	Deviation
              ↓         C      ↑                Compass

     Tele-Vision Makes Dull Children add Wonder.

     The heading must be uncorrected to provide a compass reading
     for the helmsman to steer.

Navigators Piloting and Charting Reference Card

Navigators Piloting and Charting Reference Card – Reference card with help for correcting and uncorrecting a compass, speed / time formulas and other quick hints for navigators.

More TVMDC – Practice Problems – Correcting and un-correcting the compass – 48 More TVMDC Practice Problems and TVMDC help.

Correcting Compass Error – More TVMDC Practice Problems and TVMDC help.

TVMDC Practice Problems

	01	02	03	04	05	06
T	343	002		091		004
V		005E	017W	003E	047E
M	322		200		226	352
D	003E	007W			007W
C			202	083		354

	07	08	09	10	11	12
T	193		353		004
V	017W	023E	012W	012E	021E	014W
M						005
D	003E	005W	006E	003E		006E
C		019		112	345

	13	14	15	16	17	18
T	343		183
V		007W	017E	003W	014W	018W
M	004	009		094
D		005E		006E	003W	002W
C	001		161		008	178

	19	20	21	22	23	24
T	015	079	083
V		018W	012W	023E	012E	003E
M	038			189
D	004E				004E	002W
C		100	088	195	157	355

TVMDC Practice Problem – Answers

	01	02	03	04	05	06
T	343	002	183	091	273	004
V	021E	005E	017W	003E	047E	012E
M	322	357	200	088	226	352
D	003E	007W	002W	005E	007W	002W
C	319	004	202	083	233	354

	07	08	09	10	11	12
T	193	037	353	127	004	351
V	017W	023E	012W	012E	021E	014W
M	210	014	005	115	343	005
D	003E	005W	006E	003E	002W	006E
C	207	019	359	112	345	359

	13	14	15	16	17	18
T	343	002	183	091	351	158
V	021W	007W	017E	003W	014W	018W
M	004	009	166	094	005	176
D	003E	005E	005E	006E	003W	002W
C	001	004	161	088	008	178

	19	20	21	22	23	24
T	015	079	083	212	173	356
V	023W	018W	012W	023E	012E	003E
M	038	097	095	189	161	353
D	004E	003W	007E	006W	004E	002W
C	034	100	088	195	157	355

Printer Friendly TVMDC practice sheets (pdf).

Thanks to Captain’s Nautical in Seattle for letting me use one of their compass’s and letting me spread a chart out in the middle of their store on the floor while I took the picture for the header.

Thanks for your interest in and support of boating safety

c / m

13 Responses to TVMDC – Practice – Correcting and un-correcting the compass

Bill Haimes says:

November 15, 2011 at 11:58 pm

The simpler method is to keep the gps in magnetic, Have the steering compass properly adjusted and do all plotting from the magnetic rose. True is only a problem when using a gyro. You will not be able to develop a deviation table for the hand bearing compass since it is portable. A properly adjusted steering compass should have residual deviation of less than two degrees on any heading, well within the steering accuracy of most helmsmen.

venjie paya says:

January 23, 2013 at 7:13 pm

sir can you gave me a easier method on how to solve variation and deviation error?

- captnmike says:
  
  January 24, 2013 at 2:39 pm
  
  There are some links in the original Post that should help a bit – I have a copy of the Nav. Quick Reference that I keep with me as a double check. I also always write things down in the same order – no shortcuts – the only other advice is to work a ton of problems – they get easier after a while
  
  - A says:
    
    February 14, 2013 at 6:23 am
    
    I agree with captain mike – look at the answers he provided and do the math, you’ll pick up the pattern. I’m taking the oupv online course and it did a horrendous job of explaining everything. Thanks a lot captain mike, i’m printing off your cheat sheet as well. Very helpful indeed.
  - captnmike says:
    
    February 14, 2013 at 7:42 am
    
    Glad you found this helpful – I have given many copies of the cheat sheet Navigators Quick Reference to people
Stephen Algabre Dela Cruz says:

May 28, 2013 at 8:42 am

God day sir !..,i want to clarify in the PROBLEM column 02, is the Magnetic becomes 357 or it is 003 either? and Compass was 004 or it is 010?
Thanks a lot Captain Mike, your links is awesome.
Very helpful indeed.

God bless.
🙂

- captnmike says:
  
  May 28, 2013 at 8:54 am
  
  Coll #2 – the answers are 357M & 004C
  
  (002T + 360 = 362) – (005E) = 357M
  
  357M + 007W = 364 ( 364 – 360 = 004C) = 004C passed to the helm to steer
  
Anonymous says:

August 16, 2013 at 4:47 am

T-002
V-005
M-357 WHY THESE IS THE ANSWER?
D-007
C-004

- captnmike says:
  
  August 16, 2013 at 7:58 am
  
  When you are moving from True to Magnetic (see the formula at the top of the page) you SUBTRACT EAST – since the True is 002T and we are going through 000 / 360.
  
  We need to make the math work so 360 + 002T = 362T
  
  then Subtract 005E – 362 = 357M
  
  Hope this helps.
  
  You might find this card useful Navigators Piloting and Charting Reference Card Print it out on heavy paper of contrasting color.
  
Joselito Galicia says:

August 16, 2013 at 4:55 am

WHY 357 IS THE ANSWER TO THE LETTER M?

- captnmike says:
  
  August 16, 2013 at 8:02 am
  
  Please see the answer to the question here:
  
  https://captnmike.com/2011/11/13/tvmdc-%e2%80%93-practice-%e2%80%93-correcting-and-un-correcting-the-compass/#comment-7677
  
Gising Tulog says:

December 4, 2013 at 9:30 pm

sir can u give me some hints to solve tides

- captnmike says:
  
  December 4, 2013 at 9:46 pm
  
  You can use the Rule of 12 to roughly show the change in the water level between high & low tide –
  
  Take the time between high & low (or low & high) tide times. The time between is divided into 6 intervals – the first interval the water level changes 1/12 of total, – 2nd interval 2/12 of total, 3rd interval 3/12 of total, 4th interval 3/12 of total, 5th interval 2/12th of total, 6th interval 1/12 of total.
  
  I remember it by 1,2,3,3,2,1, – bit tough to show this without a sketch – I hope this helps a bit
  
  Thanks for visiting