Learning objective: You pick the right mnemonic in the exam — CDMVT for the conversion, ANDS only on east/west, UNOS only through north/south — without swapping the stickers.
60 seconds: You are flying a westerly and you accelerate. The question is: “You accelerate on a westerly, northern hemisphere. Where does the compass swing?” If you mutter UNOS, you grabbed the wrong label. Remember: power on E/W = ANDS. Turn through N/S = UNOS. And west deviation: compass most, not “best”.
Four lines you can say out loud:
| Mnemonic | Meaning |
|---|---|
| Variation East, Magnetic least | Magnetic smaller than true |
| Variation West, Magnetic best | Magnetic larger than true |
| Deviation East, Compass least | Compass smaller than magnetic |
| Deviation West, Compass most | Compass larger than magnetic |
Conversion C → T: Compass ± Deviation = Magnetic ± Variation = True. Reverse T-V-M-D-C. Crutch: Can Dead Men Vote Twice (CDMVT).
Teaching example (not AFM): True 060°, Var 5°W, Dev 2°E → Magnetic 065°, Compass 063°.
Southern hemisphere: ANDS/UNOS reverse. The words stay English because the exam knows them that way.
“Deviation West, Compass best.” That is wrong. — best belongs to variation. People rhyme both to best; the exam line wants most.
Exam knowledge
- CDMVT: Compass–Deviation–Magnetic–Variation–True.
- East: least. West variation: magnetic best. West deviation: compass most.
- ANDS = acceleration E/W, northern hemisphere.
- UNOS = turning error N/S, northern hemisphere.
- SH reversed.
- Swap the acronym, lose the item.
Source: FAA-H-8083 and common EASA PPL crutches. Mnemonics are school, not AFM. Detail lives in the compass-errors lesson.
Check yourself
1. ANDS on a northern-hemisphere magnetic compass on east or west headings means:
- A) Accelerate North, Decelerate South
- B) Accelerate South, Decelerate North
- C) Undershoot North, Overshoot South — that is the acceleration rule
- D) Accelerate East, Decelerate West — only on north/south headings
2. UNOS when turning through north or south (northern hemisphere):
- A) Overshoot North, Undershoot South
- B) Accelerate North, Decelerate South — turning through north
- C) Undershoot East, Overshoot West
- D) Undershoot North, Overshoot South — roll out early on north, late on south
- A — ANDS on E/W. C is UNOS (turning error).
- D — UNOS: undershoot north (compass lags), overshoot south. Southern hemisphere reversed (OSUN).