A short presentation in topic "Error in Levelling with its Preventive Measures".

1. WELCOME
A presentation on:
ERROR IN LEVELLING WITH ITS PREVENTIVE MEASURES
Presented By: Presented To:
Ashim Sharma
GE(22)
Basu Dev Bhandhari
(Department of Civil and
Geomatics Engineering)

2. Error In Levelling:
1. Instrumental Errors
2. Natural Errors
3. Personal Errors
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3. 1. Instrumental errors:
 Error due to imperfect adjustment of level
- line of sight not perfectly horizontal(leads to collimation error)
 Error due to sluggish bubble
- remains central though the bubble axis not horizontal
 Rod not of standard length
- incorrect graduations of the staff
 Error due defective tripod
- instability of instrument due to shaky tripod
 Zero Error
- if the zero point of the graduation of staff is not exactly at the base of the
staff
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Fig:- Collimation Error

5. 2. Natural Errors:
 Earth’s curvature
- line of sight deviate from a horizontal line, lowers the elevation
 Atmospheric Refraction
- the line of sight is refracted towards the surface of earth in a curved path, raises
the elevation
 Variations in temperature
- expansion of the bubble due to temperature, shifting of bubble to heated end
 Wind vibrations
- high wind shakes the instrument and disturbs the bubble and the rod
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Fig:- Error due to curvature Fig:- Error due to refraction

7. 3. Personal errors:
 Mistakes in manipulation
- error in setting up the level, parallax, staff not vertical
 Mistake in reading the rod
- Reading against top or bottom hair instead of central hair
 Errors in sighting
- difficult to see the exact coincidence of the cross hairs and staff graduation
 Mistakes in recording and computing
- digits interchanged, entering B.S & F.S in wrong column, arithmetical
mistakes
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8. Error Adjustment:
We can also adjust the error by following ways:
1st method: If the distances between points are known then the correction will
be distributed over the distances.
Correction Formula: (total error*distance)/total distance
2nd method: If the distances are not known then the correction can be
distributed according to the number of instrument positions.
Correction Formula: (total error* no of instrument setup)/total no of
instrument setup
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9. Preventive Measures
Here are some methods for reducing the errors in levelling:
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• Level must always be carefully tested and adjusted before used.
• Back sights and Foresights should be made equal.
• Observing the bubble after target has been sighted.
• Rod graduation should be tested and compared with any standard
tape.
• Every screws and bolts of tripod should be checked
• For removing zero errors, levelling is started and end up by the
same staff.

10. Preventive Measures
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• Staff readings should be kept small neglecting the surface of the
earth.
• Use of umbrella to protect level and instrument.
• Avoid levelling during noon hours.
• Hold rod firmly; Use head/body to support it.
• Usual field check should be done.

11. References:
 Agor, R. (2012). Surveying and Levelling. Khanna Publishers.
 Punmia, Dr. B.C. (2005). Surveying Vol. I. Laxmi Publications.
 URL 1: http://aboutcivil.org/errors-in-levelling.html| Accessed on:
21Jan,2017
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