Module 9 - Compass
Converting Between Bearings — CADET and CDMVT
To convert between True, Magnetic, and Compass bearings, you add or subtract Variation and Deviation. The mnemonic CADET tells you whether to add or subtract: Compass + Add + Deviation + Equals + Magnetic. Then Magnetic + Add + Variation + Equals + True. When going from Compass to True, ADD easterly errors. When going from True to Compass, SUBTRACT easterly errors.
An alternative mnemonic is 'Cadbury Dairy Milk Very Tasty': Compass → Deviation → Magnetic → Variation → True. Going from left to right (Compass to True), add Easterly errors (and subtract Westerly). Going right to left (True to Compass), subtract Easterly (and add Westerly).
- CADET: Compass ADd East for True (Compass → True)
- Cadbury (C) Dairy (D) Milk (M) Very (V) Tasty (T)
- Compass → +Dev → Magnetic → +Var → True (add East errors)
- True → −Var → Magnetic → −Dev → Compass (subtract East errors)
- West errors: do the opposite (subtract when going C→T, add when T→C)
Watch for this: When in doubt, remember: 'Error East, Compass Least' — if error is East, the compass reading will be LESS than the true bearing. 'Error West, Compass Best' — compass reading is MORE than true.
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.