The Brunton Compass

©2010 Dr. B. C. PaulNote – The techniques shown in these slides are considered common knowledge to surveyors. Figures in the slides may be the authors own work or extracted from Instrument Users Manuals, Surveying by Bouchard, Mine Surveying, or various internet image sources. (Includes work done by the author in 2007)

The Brunton Compass or Pocket Transit

The Brunton is a small piece of low precision surveying equipment that can be put in your pocket, held in your hand, and used by one person to complete a simple survey

Distance measurement in a Brunton Survey is usually done by pacing

Bruntons have the ability to measure strikes and dips of rock formations so they are still valuable remote geological work (GPS units aren’t much use in measuring dip of

a rock formation)

Opening A Brunton

Raise the cover

Extend the Sighting Arm

Raise the Pointer

Working with a Brunton at Belly Level

Look down into the mirror and lineUp your target, the sighting pointAnd the line on the mirror.

Reading the BruntonUse the Bubble Level to level the Compass

The North Seeking end of the Compass Points to the Azimuth of the line of sight

Using the Brunton at Eye Level

Sight through the hole in the sighting point and the hole in the mirror(it is called a peep sight)

The Mirror Provides a View of the Compass

This time the South EndPoints the Azimuth

Taking an Incline with a BruntonPlace the Brunton on the inclinedsurface

Using the lever on the back adjust the level bubble

Reading the Scale

Read outer incline scale and add the Vernier

A Quadrant – Bearing Brunton Held at Belly Level

EW

30

I am goingNorth 30 degreesEast

A Quadrant-Bearing Compass at Eye Level

EW

60

60

Read the SouthArrow at eyeLevel

North 60 East

An Azimuth Compass at the Belly0

90 270

40

Read North arrow

Azimuth is 40

An Azimuth at Eye Level180

270 90

40

Read theSouth Arrow

Azimuth 40

Just One Little Problem

The Magnetic North Pole is not at the North Pole

This means there is a difference between true north and magnetic north

Brunton Compasses can be adjusted for magnetic declination

Example

The Magnetic Declination of Carbondale is 1º 31’ to the west Ie the magnetic pole is 1 degree 31’ to

the west of the true north pole If we use our Brunton with no

correction for declination it will point north when in fact we are aiming 1 degree 31’ to the west

Checking Declination on a Brunton

A pin shows the declinationSet on the compass

When the Pin points to 0The declination is set to 0

There is a screw on the sideOf the Brunton Compass thatRotates the scale.

If Our Declination were 15 degrees East of North

We would rotate theDial so the indexNeedle point to 15Degrees on the eastSide of north.

If Our Declination Were 15 Degrees West of North

We would adjust so the indexNeedle pointed 15 degreesTo the west of north.

Proficiency Time

Set the magnetic declination on the Brunton Compass for Carbondale Illinois.

Read the Bearing Compass at Eye Level

Read the Azimuth Compass at Belly Level

After Your Proficiency

So I know you can read direction on the compass

Layout a taped line of 100 feet on the sidewalk Walk the line (straight – no inebriation)

and count your paces Use this exercise to establish the length

of one of your paces.

Now Start a Brunton Traverse

Start at point A and retrace your way around the surveying stations you set up on your regular traverse.

Stand on Your Point Foresight your next point with your Brunton Note the direction of the line Pace out the distance to your foresight point

and note it Repeat for the next point until you

entirely close around your traverse back to point A

Things to Note

I never did a Backsight Why? The compass establishes the azimuth of the

foresight line In a conventional traverse you backsight a

known direction and turn an angle Backsight Azimuth + Angle = Foresight Azimuth

With the Brunton the compass gives you a direct read to the foresight without needing a backsight or measuring an angle turned.

Enter Your Results in the Brunton Traverse Calculator

Produce a sketch of your traverse labeling each of your points

Create a table showing the coordinates you obtained for each point by a conventional traverse and then by a Brunton Traverse