It is nice to have a rule to help with memory when finding compass errors. When correcting, easterly errors are added and westerly subtracted. When uncorrecting,add west and subtract east. An alternative method for remembering the rules of correcting and uncorrecting involves using the first letters of the following words:
Compass, Deviation, Magnetic, Variation, and True and letting these be the initial letters of words that form an easy to remember sentence. A convenient one to use is Can Dead Men Vote Twice? Using this sentence to remember the order, I write down just the initial letters vertically
C
D
M
V
T
To the left of the column, draw a double-ended arrow, placing a W at the top, and E at the bottom and a plus sign in the center. The arrow heads have nothing to do with actual direction but apply only to the direction of proceeding through the initial letters of the memory phrase, whether correcting from compass to true or uncorrecting from true to compass.
Now, by placing the given information in the corresponding blanks, the unknown values can be computed following the rule of the form. When going from compass to true add east and subtract west. When going from true to compass add west and subtract east. I will be going over more of these types of problems later when working with leeway and compass constuction problems.
