Correcting and Un-correcting a compass is still a useful skill.  Paper charts and plotted course lines are still in use, even with today’s Cell Phone Apps and GPS Plotters.   If you take a Navigation or Piloting class that lasts more than 4 hours you will need these skills.  Here are 48 more Compass Correction practice problems to help polish your skills.

“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).  Compass is the compass heading of the vessel.  Wind and current also have an effect on the Course To Steer (CTS), those outside effects are not addressed here but you need to be aware that they exist.

Variation is the difference between where a magnetic compass points and true north for a given point on the earth.  Variation is read from the compass rose on the chart. Variation is the same for all boats at the same point.  If North on the magnetic compass points to the East of True North the Variation is called EASTERLY.  If North on the magnetic compass points to the West of True North the Variation is called WESTERLY.

Deviation is the failure of the compass to point to magnetic north due to local magnetic fields on a 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.  Deviation will usually change for a boat based on the boats heading.

Compass error is the combination of Variation and Deviation.

Direction is written using three digits (000T (True), 000M (Magnetic) or 000C (Compass).

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.  NEVER 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 un-correcting a compass, speed / time formulas and other quick hints for navigators.

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

TVMDC – Practice – Correcting and un-correcting the compass – 24 more TVMDC compass correction practice problems.

Printer Friendly TVMDC practice sheets (pdf).  Printer friendly version of this exercise with answers.

TVMDC – Compass Correction Practice Problems

TVMDC Compass Correction Practice Problems

TVMDC Compass Correction Practice Problem – Answers

TVMDC Compass Correction Practice Problem – Answers

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