SOURCES OF ERRORS IN LEVELING

• INSTRUMENTAL ERRORS:

  • INSTRUMENT OUT OF ADJUSTMENT

  • ROD NOT STANDARD LENGTH

  • DEFECTIVE TRIPOD
• PERSONAL ERRORS:

  • BUBBLE NOT CENTERED

  • PARALLAX

  • FAULTY ROD READINGS

  • ROD NOT HELD PLUMB

  • INCORRECT SETTING OF TARGET

  • UNEQUAL BS AND FS DISTANCE
• NATURAL ERRORS:

  • CURVATURE OF EARTH

  • ATMOSPHERIC REFRACTION

  • TEMPERATURE VARIATIONS

  • WIND

  • SETTLEMENT OF INSTRUMENT

  • FAULTY TURNING POINTS
• COMMON MISTAKES IN LEVELING:

  • Misreading the rod

  • Incorrect recording • Erroneous computation • Rod not fully extended • Moving turning points
• 3 FIELD ADJUSTMENTS OFTEN REQUIRED FOR DUMPY LEVEL:

  • ADJUSTMENT OF THE CROSS HAIRS

  • ADJUSTMENT OF THE LEVEL VIAL

  • ADJUSTMENT OF THE LINE OF SIGHT
• the test of the line of sight of the dumpy level was illustrated by a procedure called "TWO-PEG TEST"
• CURVATURE & REFRACTION -Taken into account in levelling work since the measurements are made in vertical planes and these effects all occur in the same plane
• EARTH'S CURVATURE -A horizontal line departs from a level line by 0.0785 m in one kilometer, varying as the square of length of the line.
• ATMOSPHERIC REFRACTION -varies with atmospheric conditions. Under ordinary conditions, it is approximately equal to 0.0110 m in one kilometer, also varying directly as the square of length of the line.
• 0.0675 - Coefficient refraction