To avoid large centering error with very short legs, observations are generally made ............

When the bubble of the level tube of level, remains central ............

The stadia lines of a tacheometer are ............

The representative fraction 1/2500 means that the scale is ............

In a closed traverse the algebraic sum of deflection angle is ............

When the cross-hairs are not clearly visible ............

In route surveys, the most suitable method of contouring is ............

An invar tape is made of an alloy of ............

The horizontal angle between true meridian and magnetic meridian, is known ............