What does the compass correction card tell us?
A small card placed in the cockpit to show the compass deviation for each heading. The card reads the courses to be steered in lieu of the required headings.
What is the mnemonics for correcting magnetic compass?
TVMDC is a mnemonic for converting true, magnetic and compass headings. TVMDC is a mnemonic initialism for true heading, variation, magnetic heading, deviation, compass heading. The most common use of the TVMDC method is correcting courses during nautical navigation.
Do you add or subtract magnetic variation?
Use this mnemonic to remember that with variation west, the magnetic direction is going to be “best” or greater than true. Variation is added to true to arrive at magnetic, or subtracted from magnetic to get true. With variation east, magnetic will be “least” or less than true.
What is a compass swing?
Filters. (nautical) The process of swinging and compensating a ship or aircraft compass by determining and reducing the deviation coefficients and recording the residual deviations; now done by computer.
What is the purpose of correcting compass?
“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.
How do you use a deviation card?
A deviation card is produced after your onboard compass, usually located at the wheel binnacle, has been swung. Ideally this is done annually. The compass deviation card marks deviation, as the name suggests, for different headings. Readings are usually taken at 30 degree intervals from 000 and 360 degrees.
How do you use a fixed declination compass?
The fixed declination correction is an additional scale under the compass needle. This is used by first taking the direction with the protractor and then turning until the compass needle points at the declination scales according to the local declination. This must be done every time the compass is read.