Meaning of compass deviation card

com'pass devia'tion card"

Pronunciation: [key]
  1. a card, sheet, or the like, with two compass roses printed on it concentrically, for recording, on a given voyage, the amount of deviation for which the navigator must compensate in using the ship's compass to steer a magnetic course.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.