Checking Survey Data
After moving in a completed polygon, the data is ready to be checked before it is plotted. The difference between the forward and backward bearing should be calculated and this number be 180. If one of your bearings errors is considerable larger than the others this signifies a measurement error. This may be discarded and by taking the means of forward and backward bearings, where there is tolerable agreement, a corrected set of data is gained. Another check can be preformed by taking the sum of the internal angles of the polygon. This number should be compared with 180*n360, where n is the number of sides to the polygon. Table 2 shows a example of this calculation. 
Table 2 
Station 
Bearings 
Internal Angle 

A 
ADAB 
3633 = 
3 
B 
BABC 
21288= 
124 
C 
CBCD 
271175= 
96 
D 
DADC 
1434= 
139 


Total = 
362 
180*(4sides)360 = 
360 