In a chain surveying work of a traverse, it is necessary to apply the correction due to sag for the tape. The correction for the sag is: Cg=
1
24
(
W
P
)2L where W = the weight of the tape per span length The sign of this correction is always negative. If both the ends of the tape are not at the same level, a further correction due to slope is required. Well sinking is the work in which the units of measurement for estimation of quantitier are not identical.