Module 9 - Compass
Converting Between Bearings — CADET and CDMVT
Write C—D—M—V—T on the page and attach a sign to each error: east positive, west negative. From compass to true, Magnetic = Compass + Deviation, then True = Magnetic + Variation. From true to compass, reverse each operation: Magnetic = True − Variation, then Compass = Magnetic − Deviation.
Example C→T: 180°C, deviation 2°E and variation 3°W. Write +2° and −3°: 180 + 2 = 182°M; 182 − 3 = 179°T. Example T→C: 250°T, variation 4°W and deviation 2°E. 250 − (−4) = 254°M; 254 − (+2) = 252°C.
CADET is a direction reminder—Compass to True, Add East—not permission to skip labels. Keep intermediate magnetic working, use the deviation for the relevant compass heading, wrap results through 000°/360° and sense-check whether an east error made the compass value less than the corresponding true value.
- CDMVT preserves order: Compass—Deviation—Magnetic—Variation—True
- Compass to True: add signed deviation, then signed variation
- True to Compass: subtract signed variation, then signed deviation
- Label intermediate M and final T/C, then check direction and wrap 360°
Optional quick check
Section 4 of 5
Using east-positive signed working, convert 120°C with 3°E deviation and 2°W variation to true.
Continue studying Compass
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