Introduction

What are Surveying Instruments?

Surveying instruments are precision tools used in civil engineering and construction to measure distances, elevations, angles, and alignments accurately. They help engineers establish reference points, transfer levels, set out building layouts, and ensure that construction work is carried out according to design specifications. Proper use of these instruments minimizes errors, improves construction quality, and enhances overall project efficiency.

What This Guide Covers

This guide provides an overview of three essential surveying instruments used in construction:

Automatic Level – Used to determine differences in elevation and transfer levels accurately during construction.
Theodolite – A precision instrument used to measure horizontal and vertical angles for alignment, setting out, and surveying.
Laser Instruments – Modern surveying tools used for distance measurement, leveling, and alignment, offering faster and more accurate results.

In addition to their applications, this guide explains the components, setup procedures, operational methods, maintenance requirements, accessories, storage, transportation, and best practices for each instrument. It serves as a practical reference for site engineers, surveyors, QA/QC engineers, engineering students, and construction professionals who wish to improve measurement accuracy and ensure quality execution on construction projects.

Index

Important Terminology

Automatic Level

Setting Up the Instrument
Checks Before Using the Instrument
Instrument Operation
Determining Difference in Elevation
Station Surveying
Horizontal Angle Measurement
Maintenance
Do’s and Don’ts
Accessories
Storage
Transportation

Theodolite

Setting Up the Instrument
Leveling
Centering Using the Optical Plummet
Checks Before Using the Instrument
Instrument Operation
Horizontal Angle Measurement
Vertical Angle Measurement
Maintenance
Do’s and Don’ts
Accessories
Storage
Transportation

Laser Instruments

Distance Measuring Instrument
Multi-Directional Laser Instrument
Rotating Laser Instrument

Important Terminologies

Benchmark (BM)
- A reference point established by the Geological Survey of India (GSI) representing the actual elevation of a specific point with respect to Mean Sea Level (MSL).
Temporary Benchmark (TBM)
- A temporary reference point established on-site and used as the reference for all level measurements during construction.
Reduced Level (RL)
- The numerical representation of the elevation (altitude) of a point with respect to a benchmark.
Base Line
- The primary reference line established in one direction on a site from which all other grid lines and marking pillars are set out according to the setting-out drawing.
Setbacks
- The minimum distance between the building line and the compound wall, or the distance between two building lines.
PCC (Plain Cement Concrete)
- Plain Cement Concrete.
GFC (Good for Construction)
- Drawings approved for construction and ready to be executed at the site.
Grid Lines
- Imaginary lines shown on drawings that generally pass through the centre of columns. They are used to locate structural elements such as columns and footings.
Masonry Line
- A tightly stretched nylon thread used as a reference to indicate direction, alignment, elevation, slope, and other geometrical boundaries.
Marking Pillars
- Temporary pillars carrying markings representing particular grid lines used for setting out.
Sunken Slab
- A portion of an RCC slab constructed at a lower level than the surrounding slab, mainly provided in toilets, balconies, and terrace gardens to accommodate drainage and plumbing lines.
Structural Drop
- A slab portion lowered by 30 mm to 80 mm below the surrounding slab. It is not intended to accommodate plumbing lines.
Setting-Out Drawing
- A drawing used to locate and align a building accurately on a plot.
Building Bye-Laws
- Regulations prescribed by the local government authority governing building design and construction, including setbacks, height restrictions, ground coverage, parking requirements, road widths, and related provisions.
Handrails
- The topmost steel member running along the staircase, providing support for people using the stairs.
Balusters
- Vertical members of a staircase welded to the base plate fixed on the sides of the staircase.

AUTOMATIC LEVEL

Automatic Level (Auto Level) is an instrument used for construction and engineering leveling.

Main Components of an Auto Level

Telescope
Erect images
20x / 24x / 28x magnification (varies according to the model)
Shortest focusing distance = 0.4 m
Focusing screw to obtain a clear image of the leveling staff
Compensator
- Working range = ±15′
- Setting accuracy depends on the model
Horizontal circle with angle scale
Base plate
Foot screws
Clamp and tangent screw
Spirit level (circular bubble)

Setting Up the Instrument

Unfold the tripod.
Firmly press the tripod legs into the ground.
Adjust the tripod head to approximately horizontal.
Mount the Auto Level on the tripod.
Tighten the fixing screw securely.
Level the instrument using the foot screws.
Bring the circular bubble exactly to the centre.
The instrument is now ready for use.

Checks Before Using the Instrument

Check the Circular Bubble

Set up and level the instrument.
Bring the bubble to the centre.
Rotate the instrument by 180°.
Verify that the bubble remains at the centre.
If it moves, the instrument requires adjustment by an optical instrument specialist.

Check the Compensator

The compensator is a freely suspended component inside the Auto Level.
It automatically compensates for minor leveling errors.
Tap the instrument gently.
The image should move slightly and then stabilize.
If the image does not stabilize, the compensator requires servicing.

Check the Telescope

Ensure the image is sharp and clear.
Remove parallax by properly adjusting:
- Eyepiece
- Focusing knob

Instrument Operation

Set up the instrument.
Level the instrument accurately.
Focus the eyepiece.
Focus on the leveling staff.
Remove parallax.
Take the staff reading.

Difference in Elevation

The Auto Level is used to determine the difference in elevation between two points.

Procedure:

Take the Back Sight (BS) reading.
Take the Fore Sight (FS) reading.
Calculate the difference in level.

General relationship:

Difference in Elevation = BS − FS

Station Surveying

Station surveying is carried out by taking observations from different instrument stations to determine levels and elevations over an area.

Typical observations include:

Back Sight (BS)
Intermediate Sight (IS)
Fore Sight (FS)

These readings are used to calculate the Reduced Levels (RLs) of different points.

Horizontal Angle Measurement

The Auto Level has an inbuilt horizontal angle scale.

Procedure:

Set up and level the instrument.
Align the vertical crosshair with the first point (Point A).
Set the horizontal circle reading to 0°.
Lock the horizontal scale.
Rotate the telescope to the second point (Point B).
Read the horizontal angle displayed on the scale.

Note: It is generally advised not to use an Auto Level for precise angle measurements. A Theodolite is recommended for accurate angle measurement.

Maintenance

Keep the instrument clean.
Protect it from dust and moisture.
Clean optical parts only with lens tissue.
Store the instrument in its carrying case.
Periodically check calibration.
Avoid shocks and vibrations.

Do’s and Don’ts

Do’s

Carry the instrument carefully.
Level the instrument accurately.
Keep lenses clean.
Use the carrying case after work.
Check calibration regularly.

Don’ts

Do not touch optical lenses with fingers.
Do not expose the instrument to rain.
Do not drop or mishandle the equipment.
Do not force adjustment screws.
Do not leave the instrument unattended on site.

Accessories

Typical accessories supplied with an Auto Level include:

Tripod
Levelling Staff
Carrying Case
Adjustment Tools
Plumb Bob (where applicable)

Storage

Store in a clean and dry place.
Keep inside the protective carrying case.
Avoid excessive heat and humidity.
Remove dust before storage.

Transportation

Always transport the instrument in its protective case.
Lock all moving parts before transportation.
Handle carefully to avoid impacts and vibrations.
Never carry the instrument mounted on the tripod.

THEODOLITE

A Theodolite is a precision surveying instrument used to measure horizontal and vertical angles accurately. It is widely used for setting out, alignment, traversing, and construction surveys.

Main Components of a Theodolite

Telescope
Eyepiece
Objective lens
Horizontal circle
Vertical circle
Horizontal clamp
Horizontal tangent screw
Vertical clamp
Vertical tangent screw
Plate level
Circular bubble
Tribrach
Levelling (Foot) screws
Optical plummet
Display panel (Digital Theodolite)
Battery compartment
Handle

Setting Up the Instrument

Follow the steps below to correctly set up the Theodolite:

Step 1: Position the Tripod

Spread the tripod legs evenly.
Position the tripod approximately over the survey station.
Ensure the tripod head is nearly horizontal.
Firmly press the tripod legs into the ground.

Step 2: Mount the Instrument

Place the Theodolite on the tripod head.
Tighten the central fixing screw securely.
Ensure the instrument is firmly fixed.

Leveling

Leveling ensures that the instrument is perfectly horizontal before taking observations.

Procedure

Center the circular bubble using the tripod legs.
Adjust two foot screws simultaneously to move the plate bubble.
Rotate the instrument by 90°.
Adjust the third foot screw.
Repeat the process until the bubble remains at the center in all directions.
Rotate the instrument through 360° to confirm that the bubble remains centered.

Centering Using the Optical Plummet

The Optical Plummet is used to position the instrument exactly over the survey station.

Procedure

Look through the optical plummet.
Locate the ground reference point.
Move the tripod carefully until the point appears near the center.
Use the tribrach shifting screws (if available) for fine adjustment.
Repeat leveling after centering.
Ensure both leveling and centering are correct before starting observations.

Checks Before Using the Instrument

Before commencing work, verify the following:

Circular Bubble

Bubble should remain centered after rotating the instrument.

Plate Bubble

Bubble should remain centered after leveling.

Optical Plummet

Ensure the plummet is exactly over the station point.

Telescope

Image should be clear and properly focused.
Remove parallax before observations.

Battery

Check battery level.
Replace or recharge if necessary.

Display

Verify that the LCD display is functioning properly.

Instrument Operation

Set up the instrument.
Level the instrument accurately.
Center over the survey station.
Focus the eyepiece.
Focus the target.
Remove parallax.
Lock the horizontal clamp.
Use tangent screws for precise alignment.
Record horizontal and vertical angle readings.

Horizontal Angle Measurement

Procedure

Set up and level the instrument.
Sight the first point (Point A).
Set the horizontal angle reading to 0°00′00″ (or note the initial reading).
Lock the horizontal circle.
Rotate the telescope towards Point B.
Precisely align the crosshair using the tangent screw.
Read the horizontal angle displayed.

Repeat the observation for improved accuracy.

Vertical Angle Measurement

Procedure

Level the instrument.
Sight the target.
Focus accurately.
Remove parallax.
Read the vertical angle displayed.
Record whether the angle is above or below the horizontal plane.

Maintenance

Keep the instrument clean.
Clean lenses only with a lens cloth.
Store in its protective carrying case.
Keep away from moisture.
Avoid direct sunlight for prolonged periods.
Recharge batteries regularly.
Send for calibration periodically.

Do’s and Don’ts

Do’s

Carry the instrument carefully.
Ensure accurate leveling before use.
Remove parallax before taking readings.
Transport in the protective case.
Keep the instrument clean and dry.

Don’ts

Do not carry the instrument mounted on the tripod.
Do not force clamps or tangent screws.
Do not expose the instrument to rain.
Do not touch optical lenses with bare fingers.
Do not store the instrument in damp conditions.

LASER INSTRUMENTS

Laser instruments are modern surveying and construction tools that use laser technology to provide accurate measurements, alignment, leveling, and layout work. They improve accuracy, reduce manual effort, and increase productivity on construction sites.

The three commonly used laser instruments are:

Distance Measuring Instrument (Laser Distance Meter)
Multi-Directional Laser Instrument
Rotating Laser Instrument

Distance Measuring Instrument (Laser Distance Meter)

A Laser Distance Meter is used to measure distances quickly and accurately using a laser beam.

Applications

Measuring room dimensions
Building layout
Interior works
Quantity estimation
Elevation measurements
Site inspections

Main Components

Laser emitter
Display screen
Keypad
Measurement button
Battery compartment
Memory function

Operating Procedure

Switch ON the instrument.
Select the required measurement unit (m, ft, in).
Place the rear of the instrument against the reference surface.
Aim the laser at the target.
Press the measurement button.
Read the displayed distance.
Record the measurement if required.

Advantages

Fast measurements
High accuracy
Easy to operate
Stores measurement values
Reduces manual errors

Multi-Directional Laser Instrument

A Multi-Directional Laser Instrument projects horizontal, vertical, and cross laser lines simultaneously.

Applications

Wall alignment
Tile fixing
Ceiling installation
Plumbing work
Electrical layout
Door and window installation
Interior finishing works

Features

Horizontal laser line
Vertical laser line
Cross line projection
Self-leveling mechanism
Compact design

Operating Procedure

Place the instrument on a stable surface or tripod.
Switch ON the instrument.
Allow the instrument to self-level.
Select the required laser mode.
Align work using the projected laser lines.
Switch OFF after completion.

Advantages

High accuracy
Easy alignment
Saves time
Suitable for interior works
Reduces marking errors

Rotating Laser Instrument

A Rotating Laser Instrument projects a continuously rotating laser beam to create a complete 360° horizontal reference plane.

It is mainly used for leveling over long distances.

Applications

Building construction
Road construction
Foundation leveling
Earthwork
Large area leveling
Drainage works
Concrete floor leveling

Main Components

Rotating laser head
Control panel
Self-leveling mechanism
Laser receiver
Tripod
Battery

Operating Procedure

Set up the tripod.
Mount the rotating laser instrument.
Switch ON the instrument.
Allow the instrument to self-level automatically.
Set the required rotation speed.
Use the laser receiver for long-distance measurements.
Record the required levels.
Switch OFF and store the instrument safely after use.

Advantages

Covers a 360° working area
Highly accurate
Suitable for long-distance leveling
Saves manpower
Increases productivity
Ideal for large construction projects

Maintenance of Laser Instruments

Keep the instrument clean and dry.
Clean laser windows with a soft cloth.
Avoid dropping or subjecting the instrument to impacts.
Recharge or replace batteries as required.
Store in the protective carrying case.
Periodically calibrate the instrument.
Protect the instrument from dust and moisture.

Do’s and Don’ts

Do’s

Read the user manual before operating the instrument.
Verify calibration before use.
Use a stable tripod or surface.
Store the instrument in its carrying case.
Handle with care during transportation.

Don’ts

Do not look directly into the laser beam.
Do not expose the instrument to heavy rain or water.
Do not drop the instrument.
Do not operate with a low battery.
Do not use a damaged instrument.

Accessories

Typical accessories supplied with laser instruments include:

Carrying Case
Tripod
Laser Receiver
Target Plate
Batteries
Charger
User Manual

Storage

Store in a clean and dry location.
Keep inside the protective carrying case.
Avoid exposure to direct sunlight and excessive heat.
Remove batteries if the instrument will not be used for a long period.

Transportation

Always transport the instrument in its carrying case.
Lock all movable parts before transportation.
Protect from shocks and vibrations.
Never transport the instrument while mounted on the tripod.

End of Chapter – Surveying Instruments

Frequently Asked Questions (FAQs)

1. What is an Automatic Level used for?

An Automatic Level is a surveying instrument used to determine differences in elevation between points. It is commonly used in construction for leveling, site layout, and transferring benchmark levels.

2. What is the purpose of a Theodolite?

A Theodolite is a precision surveying instrument used to measure horizontal and vertical angles. It is widely used for alignment, setting out, and construction surveying.

3. What are Laser Instruments used for in construction?

Laser instruments are used for accurate distance measurement, leveling, alignment, and layout work. They improve efficiency and reduce manual measurement errors on construction sites.

4. What checks should be performed before using surveying instruments?

Before use, ensure the instrument is properly leveled, verify the bubble level, remove parallax, inspect the optics, check the battery (for digital instruments), and confirm calibration for accurate measurements.

5. How should surveying instruments be maintained?

Surveying instruments should be cleaned regularly, stored in their protective carrying case, protected from dust, moisture, and impacts, and calibrated periodically to maintain measurement accuracy.