From the plan (fig 1), the center line of the walls are calculated. Then the center lines of the rooms are set out by setting perpendiculars in the ratio 3:4:5. Suppose the corner points are A, B, C, D, E, F and G which are marked by pegs with nails on top.

The setting of the corner point is checked according to diagonals AC, BD, CF and EG.

During excavation, the center points A, B, C, D, E, F, G may be removed. Therefore the center lines are extended and the center points are marked about 2m away from the outer edge of excavation. Thus the points A1, A2, B1, B2 and likewise, are marked outside the trench. Centre line are shown clearly by stretching thread or rope. The center points fixed 2m away from the excavation are marked with sit out pegs.

From the plan details, the width of excavation to be done is also marked by thread with pegs at appropriate positions.

The excavation width is then marked by lime or by with furrow with spade.

A theodolite should be used for accurate center line marking.