Module 9 - Compass
Deviation
Deviation is the error caused by magnetic influences on YOUR boat — the engine, electronics, metal fittings, and even a mobile phone near the compass can deflect the needle. Unlike variation, deviation is different on every heading.
Deviation is recorded on a deviation card (or table), which shows the deviation for different compass headings. It is determined by 'swinging the compass' — comparing known bearings with compass readings on various headings. Deviation should be small (ideally under 5°) if the compass is properly adjusted.
- Deviation = compass error caused by the boat's own magnetic field
- Different on every heading (unlike variation, which is constant for an area)
- Recorded on a deviation card for your specific boat
- Minimised by adjusting the compass (placing corrector magnets)
- Keep metal and electronics away from the compass
Continue studying Compass
This public lesson is part of Revision Module 9. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.