1.  The concept of monitoring is to measure the displacement of fixed prisms.
 2.  Targets (Prisms)will be fixed on selected critical points on the structure or area.
 3.  Position (X,Y,Z)of prisms will be surveyed to produce a set of reference positions.
 4.  From time to time, the position of the prisms will be measured.
 5.  The latest observed position is then compared with the initial reference positions.

Theoretically, if there has been no movement, the position of the fixed prisms will never change. Therefore, if there is any difference between measured position and fixed position, it indicates presence of movement.

The main advantage of this system is it indicates the SIZE OF MOVEMENT as well as DIRECTION OF MOVEMENT.