1.0 INTRODUCTON

Leveling may be the art of determining the relative heights or elevations of points are objects

on the earth’s surface. It deals with measurements in a vertical plane.

Definitions of terms used in Leveling:

1. A level surface:

It is any surface parallel to the mean spheroidal surface of the earth e.g. surface of a still lake.

Since the earth is a oblate spheroid, a level surface may be regarded as a curved surface,

every point on which is equidistant from the center of the earth. It is normal to the plumb line

at all points.

2. A level line:

It is line lying in a level surface.  It is therefore, normal to the plumb line at all points.

3. A horizontal plane:

It is a plane tangential to the level surface at that point. It is perpendicular to direction of

gravity (plumb line).

4. A horizontal line:

It is any line lying in the horizontal plane. It is a straight line tangential to a level line.

5. A vertical line:

It is a line normal to the level surface through that point e. g. a plumb line.

6. A vertical plane:

It is a plane containing a vertical line.

7. A vertical angle:

Angle between two intersecting lines in a vertical plane, one of the two lines is commonly

taken as horizontal in surveying.

8. A datum surface or line:

It is any arbitrarily assumed level surface or line from which vertical distances are measured

in India the datum adopted for G.T.S. bench marks is the mean sea level at Karachi now in

Pakistan.

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9. The elevation:

It is vertical distance of a point above or below the datum. It is also known as the reduced

level (R.L.) The elevation of a point is plus or minus according as the point is above or below

the datum.

10. The difference in elevation (H):

It is the vertical distance between the level surfaces passing through the two different points.

11. A bench mark (B.M.):

It is fixed reference point of known elevation.

12. The line of collimation:

It is the line joining the intersection of cross hairs of the optical center of the object glass. It is

also called the line of sight.

13. An axis of the telescope:

It is a line joining the optical center of the object glass to the center of the eye piece.

14. Foresight:

(Also called a foresight reading) It is a staff (or rod) reading on a point whose elevation is to

be determined or on a change point. It is also termed as minus sight. It is the last staff reading

denoting the shifting of the instrument.

15. An Intermediate sight (I. S.):

It is any other staff reading taken on appoint of unknown elevation from the same set up of

the level. All sights taken between the back sight and the fore sight and the foresight are

intermediate sights.

16. A change point (C. P):

It is appoint denoting the shifting of the level. It is a point on which is the fore and back

sights are taken. Any stable and well defined object such as a boundary stone, curb stone rail,

rock etc. is used as a change point. A bench mark may also be taken as a changer point. It is

also called a turning point (T. P).

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17. A Station:

It is a point whose elevation is to be determined. It may be noted that it is a point where the

staff is held not the point where they leveled is set up.

18. The height of instrument (H. L):

It is the elevation (or the R.L.) of the plane of collimation (or plane of sight) when the

instrument is correctly leveled. It is also called the height of plane of the collimation.

To determine elevation of points two instruments are required, viz.

1. A level

2. A leveling staff or rod.

The level:

Level consists of essentially

1. Leveling head

2. The limb

3. Telescope

4. bubble tube

Types of level:

1. Dumpy level

2. y level

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2.0 OBJECTIVE

1. To get the perfect reading on the instrument

2. Recalibrate levelling instrument and staff so, the reading levelling is suitable to the

height of the earth surface

3. Diffrentiate the damage instrument on value reading for send to the supplier

4. The first procedure to prevent the error in the process of leveling gone wrong.

3.0 THEORY

The purpose of the test is to know the accurancy of the leveling instrument. It also can

find the error and the damages on the instrument. Other than that, before doing the test, we

must make sure the calibration of the instrument is perfect. So, the real distance does not have

big difference than the distance that taken during the test.

Distance from the front view to the leveling instrument must not be too far to reduce the error

on collimation. Besides, this test will be succeed and granted if the real distance smaller than

the limit distance allowed. The minimum distance after the front view staff is 6m and the

maximum is 66m.

Front view staff is the last before tranfering the instrument from the CP to the next

CP. BM which is Benchmark is the fixed station on the earth surface.

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4.0 INSTRUMENTS

There were several instruments that used for running Two Peg Test and Levelling.

Two Peg Test :-

1. Level and Tripod ( 1 set )

A level is required to define the reading of vertical distances on the staff.

2. Staff ( 2 set )

A levelling staff is needed to measure vertical distances.

3. Staff bubble ( 2 set )

Staff bubble is fitted to the staff to make sure the staff stable to the ground.

4. Measuring Tape

A tape is used to measure distances between the level and staff.

Levelling :-

1. Level and Tripod ( 1 set )

A level is required to define the reading of vertical distances on the staff.

2. Staff ( 2 set )

A levelling staff is needed to measure vertical distances.

3. Staff bubble ( 2 set )

Staff bubble is fitted to the staff to make sure the staff stable to the ground.

4. For measuring distances for levelling, not using tape but using foot step.

5. Hammer

6. Nail / Thumbtack

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Level and Tripod

Staff

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Staff bubble

Measuring tape

5.0 PROCEDURE

Two Peg Test procedure :-

1. Measure out 3 points (Point A, B and C) which is 30m apart, and mark them on

the ground. Point A as back sight and point C as foresight.

2. Set up the level instrument at point B, the centre and put the staff at point A and

point C.

3. To set up the level, first set up the tripod. Ensure the top is level. Push legs firmly

into the ground. Then, attach level. Use the foot screws to centralise the circular

bubble. Test to see if the compensator is working and the remove the parallax to

see clearly.

4. Make sure the stuff bubble is at centre of the circle to get the right readings.

5. Read the staff vertical distance at point A, record the data and read again.

6. Rotate the level to point C, read the staff reading at point C, record the data and

read again.

7. Move the level instrument to 6m beyond point C on the line point A,B and C.

8. Set up the level, read the staff at point A and record the data. Then, read the staff

at point C and also record the data.

9. Calculate height difference.

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CA

30m 30m

B6m

Levelling procedure.

Observing procedure :-

1. Levelling depends on area given. For group 2, the area involve are K4, K5, K6, K7

and K8.

(Practical Area)

2. Start at TBM 1 area K4, put the staff at TBM 1. Using footsteps, 39 steps as 30m.

From TBM 1, measure 39 steps and set up the level instrument at the point. Measure

another 39 steps and it will be the change point, (Point A). Put another staff at Point

A.

3. Read the first staff at TBM 1, it is a back sight reading and record the data in the

Levelling Observation form. Rotate the level to Point A, it will be foresight reading.

Read the staff at Point A and record the data.

4. Next, move the level instrument 39 steps from Point A and measure Point B. Put the

staff from TBM 1 at Point B. The staff at point A will stay. Set up the level, read the

staff at point A and record the data as back sight reading. Rotate the level towards

Point B, read the staff and record the data.

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5. Move the level instrument with the same distance from Point B. Set up the level and

measure Point C. Put the staff from Point A to Point C. Read the staff at Point B,

record the data. Rotate the level to Point C, read the staff and record the data.

6. Move again the level instrument with the same distance from Point C. Set up the level

and measure Point D. Point D is the TBM point. Mark the Point D using the hammer

and nails given. Put the staff from point B to Point D. Read the staff at Point C, record

the data. Rotate the level to Point D, read the staff and record the data.

7. Move the level instrument with the same distance from Point D. Set up the level and

measure Point E. Put the staff from Point C to Point D. Read the staff at Point D,

record the data. Rotate the level to Point E, read the staff and record the data.

8. Next, move the level instrument with the same distance from Point E. Set up the level

and measure Point F. Put the staff from Point D to Point F. Read the staff at Point E,

record the data. Rotate the level to Point F, read the staff and record the data.

9. Move the level instrument with the same distance from Point E. Set up the level and

measure Point F. Put the staff from Point D to Point F. Read the staff at Point E,

record the data. Rotate the level to Point F, read the staff and record the data.

10. Next, move the level instrument with the same distance from Point E. Set up the level

and measure Point F. Put the staff from Point D to Point F. Read the staff at Point E,

record the data. Rotate the level to Point F, read the staff and record the data.

11. Move the level instrument with the same distance from Point F. Set up the level and

measure Point G. Put the staff from Point E to Point G. Read the staff at Point F,

record the data. Rotate the level to Point G, read the staff and record the data.

12. Lastly, move the level instrument with the same distance from Point G. Set up the

level and the other Point H is back to the TBM 1. Put the staff from Point F to TBM 1.

Read the staff at Point G, record the data. Rotate the level towards Point H (TBM 1),

read the staff and record the data.

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Booking procedures :-

1. The Rise and Fall Method

The terms that are commonly used in the Rise and Fall Method are:

BS = Back sight, FS = Foresight, IS = Intermediate Sight, and RL = Reduced Level.

2. Height of Collimation

Height of Collimation (HOC) = Reduce Level (RL) + Back sight (BS)

Height of Collimation (HOC) – Foresight (FS) = Reduce Level (RL)

Calculation procedures :-

1. Checks survey accuracy, and should be within tolerances given below.

2. The following check the arithmetic of your level reductions and must be exact:

∑ BS - ∑ FS = ∑ Rise - ∑ Fall

(Back sight) – (Foresight) = (RL) (last BM) – RL (start BM)

3. Misclosure should be:

±(20√D) mm, where D is the length of the traverse in km.

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