Adjustments and Corrections:

It may be noted that the presence of local attraction will affect all the bearings taken at a particular station in the same way. Hence, the difference between the bearings of lines recorded at a particular station, giving the included angle between the survey lines will have the correct value even when the station is observed to have the local attraction disturbances.

The corrections within the recorded bearings at a station influenced through local attraction could be made through either of the following methods.

(a) The difference between fore bearings and back bearings of all the survey lines are determined. The line having a variance of exactly 180^o is selected as unaffected line. The magnitude and direction of error, i.e. the deviation from 180o and its sign (+ ve if more than 180^o and - ve if less than 180^o) at other stations is determined. The corrections are thus applied to other survey lines with reference to unaffected line.

(b) Included angles of all the survey lines are computed for closed traverses. The sum of these included angles shall be equal to (2n - 4) right angles, while n is number of survey lines in the traverse. The error if any in the sum of included angles is then distributed either equally or in proportion to the magnitude of angle, to all the angles once again starting from the unaffected line. The bearings of other lines are corrected by taking the corrected values of included angles.

(c) If no line can be located which has a 180^o difference between its fore and back bearing, the survey line along with minimum deviation is selected and the error is equally applied in fore bearing and back bearing to bring the difference to exactly 180^o. The bearing of other lines are then corrected following the procedure discussed above.