Offset Measurements:

As discussed previously, the chain survey is begin with measurements along base line and extended along all the frameworks of survey lines. The laying of chain line and making measurement of distances along the survey line were elaborates in earlier section. The next significant part of distance measurement is locating the important details of features in the vicinity of survey lines by means of offsets. Offsets up to or less than 15 m from the survey lines are commonly termed short offsets although those larger than 15 m are called long offsets. In general course of chain surveying, perpendicular offsets are measured. An Oblique offsets are recorded only in exceptional cases when it is difficult to obtain normal offsets or else these are absolutely essential.

Perpendicular offsets could be set either (a) manually or (b) with the help of offset instruments like cross staff or optical square.