Mistakes in ComputationsAn involved computation, such as determining anarea by DMDs, involves a large number of calculationsthat present the possibility of a large number of errors.Some of the most common types of mistakes arediscussed below in the hope that, if you know what theyare, you may be able to avoid them.MISTAKES WITH SIGNS.— You must beextremely careful to give a value (such as a latitude ordeparture) its correct sign in the first place and to applythe sign correctly in addition, subtraction, multi-plication, and division. The matter of signs is such afertile field for mistakes that a good idea is never to writea value without including the sign. The practice ofomitting plus signs is a correct procedure, but it is saferto write in the plus signs. Then, if you find a valuewithout a sign, you know that you forgot to put the signin and that it might just as possibly be a minus as a plus.WRONG COLUMN.— A WRONG COLUMNmistake may be an entry made in a wrong column or areading taken from a wrong column. To avoid suchmistakes, make both entries and readings withdeliberation; that is, without undue haste and alwayswith close attention to the column in which it should beentered or read.WRONG QUADRANT.— When you mistake thequadrant in which a line lies, you get a bearing that mayhave the correct angular value but that has the wrongcompass direction. The usual mistake of this kind is toset down the compass direction of the back bearingrather than of the front bearing.A common cause of this mistake is viewing thedirection of a line from the wrong station. In figure 740,the direction of AB is northeast but the direction of BAis southwest. AB and BA are, however, the same traverseline. But if you are determining the direction of AB, thatdirection is northeast. But if you are determining thedirection of BA, that direction is precisely the opposite,or southwest. To minimize direction error, you mayplace arrows on the diagram showing the direction ofthe line.WRONG AZIMUTH.— The same considerationapplies to azimuths. Suppose that the bearing of AB infigure 7-40 is N46°E. Then the azimuth of AB is(measured from north) 46°. BA is the same traverse line;but the azimuth of BA is definitely not 46°, but 226°.LEAVING OUT A TRAVERSE LINE.— Acommon source of mistakes is leaving out (commonlycalled dropping) a traverse line, either in the field notesFigure 7-40.—Proper compass direction of a closed traverse.or in computations. If you get an outsized angular andlinear error of closure, you check first to make sure thatyou have not dropped one of the traverse lines.WRONG DECIMAL PLACE.— The incorrectplacement of a decimal point is a common mistake.Suppose, for example, you are determining anapproximate double area by multiplying a DMD of+841.97 feet by latitude of –153.53 feet If you were tomistakenly use a value of –1535.3 instead of the correct–153.53, you obviously will not arrive at the correctresult.Locating MistakesIf you cannot locate and correct a particular mistake,you must rerun the whole traverse to find it. However,this can often be avoided if you know a few tricks forlocating mistakes.OUTSIZED ANGULAR ERROR OF CLO-SURE.— The size of an outsized angular error ofclosure may be a clue to the location of the particularmistake. Suppose, for example, that for a six-sidedclosed traverse, you measure interior angles as follows:90°18'118°48'154°42'147°18'101°12'612°18'The interior angles in a six-sided closed traverseshould add up to 720°00'. The difference between720°00' and 612°18' is 107°42'. This large differencesuggests that you dropped an angle measuring about7-27