Drawing, Setting Out and Levelling
Drawing, Setting Out and Levelling tests reading plans, elevations and sections, using scales, transferring dimensions to ground, establishing a datum and checking levels with a dumpy level or total station.
Core rules
- A plan is a horizontal view; an elevation is a vertical face; a section is a cut view. Check the stated scale before scaling any dimension.
- Set out from a fixed benchmark or datum, not from a temporary peg that may move.
- For a rectangular building, check both diagonals; equal diagonals confirm square corners.
- The 3-4-5 method gives a right angle: 3 m one way, 4 m the other, and 5 m diagonally.
- With a dumpy level, take a backsight on a known benchmark, calculate height of instrument, then take foresights; reduce levels by height-of-instrument or rise-and-fall.
Worked example
Set out a 6 m × 8 m rectangle. The diagonal is √(6² + 8²) = √100 = 10 m. Mark one corner, measure 6 m along one axis and 8 m along the other, then adjust the pegs until both diagonals read 10.00 m. This is the 3-4-5 triangle multiplied by 2. Check the diagonals again after fixing the profiles.
Traps that cost marks
Checking only one diagonal, measuring from a moving peg, or misreading the staff by one metre are common. Do not scale a drawing when a written dimension is given; written dimensions govern.
Key points
- Equal diagonals confirm a square rectangle.
- 3-4-5 gives a right angle; 6-8-10 is the same triangle doubled.
- Set out from a stable benchmark, not a temporary peg.
- Height of instrument = reduced level of benchmark + backsight.
- Written dimensions override scaled measurements.