meters (this falls in the fourth [northwest] quadrant), compute the dN and the dE.

t. Accuracy and Specifications. The overall accuracy of a traverse depends on the equipment, the

methods used in the measurements, the accuracy achieved, and the accuracy of the starting and closing

data. An accuracy ratio of 1:5,000 is the minimum accuracy sought in topographic surveying. In

obtaining horizontal distances, an accuracy of at least 2 millimeters per 100 meters must be obtained.

When using a 1-second theodolite, surveyors turn the horizontal angles twice in each position (two

direct and two reverse observations) with an angular closure of 10 seconds per station.

u. Linear Error. To determine the acceptability of a traverse, surveyors must compute the linear

error of closure (LEC) (using the Pythagorean theorem), the AE, and the accuracy ratio. The first step in

either case is to determine the linear error in dN and dE. In the case of a loop traverse, the algebraic sum

of the dNs should equal zero. Any discrepancy is the linear error in dN. The same is true for dEs.

Surveyors then compute the AE using the appropriate accuracy ratio (1:5,000 or better) and the total

length of the traverse. Compare this to the LEC. If the AE is greater than the LEC, the traverse is good

and can be adjusted. If it is not good, it must be redone.

v. Accuracy Ratio. The accuracy ratio provides a method of determining the traverse accuracy and

comparing it to established standards. The accuracy ratio is the ratio of the LEC (after it is reduced to a

common ratio and rounded down) to the total length of the traverse. If the accuracy ratio does not fall

within allowable limits, the traverse must be redone. It is very possible that the measured distances are

correct and that the error can be attributed to large, compensating angular errors.

w. Coordinate Adjustment. Surveyors make adjustments to the traverse using the compass rule.

The compass rule states that on any leg of the traverse, corrections to the dN or the dE are also

corrections to the total correction for the dN or the dE, as the length of the leg is to the total length of the

traverse. The total correction for the dN or the dE is numerically equal to the error in northing (En) or

the error in easting (Ee) but with the opposite sign.

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