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30 served in applying the deviation to the correct magnetic course to obtain the compass course as were employed in applying the variation to the true course to obtain the correct magnetic course; also that the same system of notation should be adopted in num- bering the points or degrees of the compass as calculated according to their position right or left of north and south. : Remember that two Ls or two Rs are to be added; an L and a R to be subtracted, in converting a correct magnetic course to a compass course. - Easterly deviation is subtracted in the NE and SW quadrants and added in the NW and SE quadrants; west- erly deviation is added in the NE and SW quadrants and subtracted in the NW and SE quadrants. o is either north or south, and 8 points or 90°, is either east or west. When the correction amounts to more . than 8 points or 90° take it from 16 points or 180°, and change N tto S, or = to N. and L-to RB; ot R to L. If the deviation being subtractive ex- ceeds the amount from which it is to be taken take the points or degrees comprising the course from the de- viation, or simply take the course from the deviation, and name it R if it had previously been ls, but towards the L -- if it had been R. A number of examples of each kind will explain this: The correct magnetic course is NE, the deviation being % point easterly, what is the compass course cor- responding thereto? Correct Mag. course NE=4 pts. Rof N Dey. Ely (sub). .:.:. oo oes 344" RoiN [=NEYN The correct magnetic course is S$ by E % E, deviation 1% points west- erly, what is the corresponding com- pass course? Cor. Mag. Co. SbyE3%,E=1% pts. Lof S$ Compass Course Dey. Wily. (sub)...... 4 2OR Compass Course fo yo Aor [=S4E C. M..C. NNE=2 pts. R of N Dey Ely (--) 2. L Comp. Course o--North Cor. Mag. Co. S by E=1pt.LofS Dev. Wly. (--) I oR Compass Course o=South C. M. C..W by S=7 pts. RofiS Dey wiv @r) i R Compass Course 8 " RofS=West C.M.C.N 4% E=¥% pt. Rof N Dev. Ely. (--) % pt. L Compass Co. , such deflections? TRAE MarRINeE REVIEW degrees, turn the course into degrees if expressed in points, and proceed as follows: The correct magnetic course is W by N, deviation 6° easterly, what is the compass course? Cor. Mag. course W by N=79° L of N ¥% pt. L of N=N 4% W Here the deviation exceeds the amount of the course, and being sub- tractive the course is taken from the deviation and the course reckoned the other way, that is, to the left. Cor. Mag. Co. ESE=6 pts. L of S Dev. Ely. (+) GL | ._ & M.S ----n . ~ ee : > to Sy ee te a ¢ TRUE iin / = NW VELL EY ayo re ay "ity We: A Baas My So ; \\ Lo, 0%, : '7 Te SS 4, OZ. + Cee S se => as A ou pee => a4. = 26 SS a= = = Ss oe ee > s= a ~-- S ZO 4 ~ S Z ~o o : RS 9 . NS S Uy, / \ S "yy fo 4, / S aa i \ \As SAS lyfe DT LAVA A S| OS "yh <0 Bee 20 \\W Li | 10 yan "uthautntin kwh Supposing it was desired to make good a true course of N 28 degrees E, with a 'Var. of 6% degrees Wly. and a Dev. of 12 degrees Ely. What course must we steer by-a compass having Now, if we did not allow for the Var., but steered N 28 degrees E (suppose we had no deviation) we would be steering 6% degrees to the left of the place we were supposed to be heading for. Very well, if the Var. will carry the ship to the left we can counteract the effects beforehand by allowing it to the right of the true course we desire to steer. 614 degrees to the right of N 28 degrees E is N 34% degrees E, which is the correct magnetic course, and also the compass course if there were no Dev., but the above figure shows that.the needle of the compass is deflected about 12 degrees to the right or Ely. of magnetic north owing to the magnetism of the ship, hence we must apply that to the left of our correct magnetic course to produce the compass course, since an Ely. deflection of the needle will carry the ship to the right of the course steered if not taken into account; therefore, we allow this Ely. deflection to the left, and 12 degrees to the left of N 34% degrees E is N 22% degrees E, or NNE, which represents the compass course to be steered in order to make good a true course of N 28 degrees E with 6% degrees Wly. Var. and 12 degrees Ely. Dev. Imagine yourself standing in the center of the compass: card looking over the point of the compass to be corrected or steered, and reason out why you allow the Var. and Dev. to the right or to the left, as the case may be. If you will.do this you will be making your own rules, rules that will suggest themselves, and they will not need memorizing, Dev. Ely. (+) a ie -- i Compass Course Compass Course. 8 "* LofS=East Cor, Mag. Co, E by N=-7" pts. R of N 85° L of N= [W YN, nearly. The correct magnetic course is S by Dev. Wly. (+) 24 OR E 3% E, deviation 15° westerly, what ee is the compass course? (exceeds 8 pts.) 0% Cor. Mag. Co. Sby E34 E=20° LofS 16 --) Dev, Why. (--) coo Compass Course 634 pts. LofS= Compass course SL ors [ESE 34 E [=SUE When the deviation is expressed in The correct magnetic course is N