Keeping the instrument height as 1.5 m, length of staff 4 m, the slope of the ground as 1 in 10, the sight on the down-slope, must be less than

Set up your level at LS1 and take a backsight reading on the bench-mark (BM). Then, take foresight readings on as many base-line points as possible. From this, find the height of the instrument (HI) and point elevations, with HI = E(BM) + BS and E (point) = HI- FS.