The following levels were taken with a metric staff on a series of pegs at 100-m intervals along the line of a proposed trench.
If the trench is to be excavated from peg A commencing at a formation level of 26.5 m and falling to peg E at a grade of 1 in 200, calculate the height of the sight rails in metres at A, B, C, D and E, if a 3-m boning rod is to be used.
Briefly discuss the techniques and advantages of using laser beams for the control of more precise work.