Manual Offsets:

Manual offsets are acquired directly without the help of any instrument by following procedures:

3-4-5 Offset

Perpendicular offset of chain line at some point A is obtained using the following mathematical expression (3² + 4² = 5²). A point B is located on chain line at a distance of 3 m from A such that AB = 3 m. Further, an arc is set on ground with centre at A and radius equal to 4 m. Another arc is laid with center at B and radius equal to 5 m intersecting the previous arc at C as shown in Figure(a). Line AC will then be perpendicular to line AB.

Figure: Manual Offset