▪ Two Peg Test is a surveying operation carried out to determine whether the levelling bubble and telescope line of sight are parallel.
▪ Peg Test is a surveying operation carried out to determine if the leveling bubble (bubble axis) and telescope line-of-sight (line of collimation) are parallel.
▪ By using the leveling method, work for establishing Temporary Bench Mark (TBM)
▪ Bench Mark (BM) must be known first. BM point determined by Land Surveyor is final.
▪ Distances between backsight and foresight must be more or less equivalent to avoid collimation errors.
▪ The survey work is to ensure so that the true error is smaller than the permissible error.
▪ Bench Mark (BM) is a fixed point on the Earth surface which its level is known height of collimation is line of collimation level from datum.
▪ Temporary Bench Mark (TBM) is a nearest point as reference if the Bench Mark (BM) is far from surveying area.
▪ Backsight is the first sight taken after temporary leveling of the instrument has been carried out.
▪ Foresight is last sight taken before the instrument is transferred to another point.
▪ Level and Tripod (1 set)
▪ Staff (2 sets)
▪ Staff bubble (2 sets)
▪ Tape (1 set)
▪ Each group will be required to perform a peg test to check the instrument.
▪ Each person in the group should record the results of the Peg Test in their own field book.
▪ Set out and mark on the ground (with wooden pegs driven into the Earth, or roofing nails in tar) two point some 30 m apart.
▪ Set up instrument midway between two pegs [setup 1].
▪ Read staff on each peg (backsight and foresight), and calculate height difference.
▪ Next, move instrument about L/10 = 3 m beyond one of the pegs (normally fore staff position, [setup 2]