T=C-W
By Lieut. Commander James C. Van de Carr, U. S. Navy
Recently, in working out a problem in Compass Error (and after looking it up in "Muir" to make sure), the writer happened to jot down the above expression and was immediately impressed with the familiarity of the term "C—W," as being one with which every navigator has wrestled in an effort to get his G. M. T. By placing a "T" on the other side of an equation from "C—W" it is promised that no navigator need ever again scratch his head, draw circles and arrows, or desperately try to remember how to apply the old rule of "true, right, east," in connection with compass work. Think it over.
T=C-W,
or true course equals compass course minus westerly error.
The "—W" suggests "+E" and it is easy to write down
T=C+ E,
or true course equals compass course plus easterly error.
The above two formulas, which amount to thumb rules by remembering "C—W," will solve any problem in connection with compass work. As an example, the navigator gets an azimuth of the sun and finds that it bears 100 (psc). The azimuth tables show that it bears 105 (true). Jot down:
T=C-W and T=C+ E.
and therefore the compass error is 5E.
Again, it is desired to steer a certain course, say 150 (true); the compass error (variation and deviation combined) is 5W.
T=C-W and
150=155-5W.
The compass course is therefore 155.
The above "Wrinkle" has been so enthusiastically received, and it is so easily applied that the writer apologetically offers it to the service in spite of its elementary nature. It is especially useful in taking temporary and reserve officers over some of the rough places in navigation, where the more fortunate of us "fit, bled, and died" in our youth.