Swing Offset:

The perpendicular distance of an important feature, e.g. building corner, from the chain line is measured using swing offset method. The zero end of tape is kept at point of interest and point A (i.e. general from C on chain line) is located through swinging the tape along with C as center. The point A is characterized by a point at which the arc generated by swing is tangential to survey line and the distance of C from any point on chain line is minimum.

It might be remembered that usually only small offsets can be set by manual methods.