Brunton Pocket Transit Instruction Manual
© 1997, The Brunton Company
BEFORE YOU START!
The following instructions will be helpful and informative. Please read them before using your transit to get the most form your investment. Once again, thanks for purchasing Brunton products.
To open your pocket transit, pull apart the sight-hinge side from the base of the transit as shown in the illustration.
To protect you transit mirror from accidental breakage while stored in its carrying case, we recommend inserting the closed transit so the base is placed against the closing snap.
Why is the bottom plate on the Brunton Pocket Transit reversed? (EAST & WEST are turned around)
REMEMBER!! The Brunton Pocket Transit is a direct reading compass.
IF YOU POINT THE NORTH END OF THE COMPASS (LARGE SIGHT END) TOWARD THE OBJECT YOU ARE OBTAINING THE BEARING TO - READ THE NORTH END OF THE NEEDLE (THE WHITE TIP). IF YOU POINT THE SOUTH END OF THE COMPASS (COVER HINGE SIDE) TOWARD THE OBJECT YOU ARE OBTAININING THE BEARING TO -- READ THE SOUTH END OF THE NEEDLE (THE BLACK TIP)
INTRODUCTION
The Brunton Company has been building professional grade field compasses since 1896 and has a reputation for perfection in directional instrumentation. Your new Brunton compass is the very best compass that can be purchased. It is a rugged, durable instrument that willwithstand the rigor associated with outdoor use by sportsmen and professionals.
The instrument is not just a compass, but combines the principles of a surveyor’s compass, a prismatic compass, a clinometer, a hand level, and a plumb. It is used to determine azibuth angles or compass bearings (and thus determine horizontal angles), to measure vertical angles, percentage of grade or slope, to run levels and measure the inclination of objects.
COMPASS DESCRIPTION
Your compass contains a magnetic needle that aligns itself with the earth’s magnetic field. This causes the needle to point to the magnetic North Pole of the earth. The needle is induction damped which allows the needle to seek north and come to a complete rest in a minimum amount of time without degrading the accuracy of the reading.
The azimuth or bearing is read directly on the compass circle with the compass needle acting as the pointer. This direct treading method is known to be the most accurate way to obtain an angle with a magnetic compass. However, with this method the compass circle is numbered in reverse. East and west are therefore interchanged and thenumbers run from 0° to 360° counter clockwise. This allows the magnetic needle’s north seeking top to point directly to the angle on the compass circle to which the large site of the compass is pointing. Figure 1 shows the instrument and its important parts.
360 Degree Graduations
This instruction manual illustrates the 360° graduated circle. With this system, North is 0° , and increases counter-clockwise, so East is 90° , South is 180° , West is 270° , and North is 360° . Of course, 360° and 0° are the same direction: North.
Quadrant Graduations
With quadrant graduations, North is 0° and increases clockwise so east is 90° , then it decreases so that south is 0° , then increases so west is 90° , and then decreases so north is 0° . The instruction in this manual also apply to this type of graduation except it is necessary to refer to the proper quadrant. As an example, North 30° East, or North 25° West, of South 35° West , of South 15° East.
The magnetic needle of your compass points to the Magnetic North Pole. The Magnetic North Pole is located in the upper Hudson Bay region and its position changes slightly from year to year. The True North Pole is located geographically. Maps and directions are based on True North since it never changes. The angle between Magnetic North and True North is called Magnetic Declination. Figure 2 shows the different declination angles for the United States.
When True and Magnetic North are the same direction, the declination is zero. As figure 2 shows, the line of zero declination passes through Western Wisconsin and off the western border of Florida. On the esat side of the zero declination line your compass will point west of True North. This is called a Westerly Declination . On the east side of the line, the compass will point east of True North. This is called Eastery Declination. As an example, if you were using your compass in Texas where the declination line is 8° , the magnetic needle would point 8° to the east of the True North Pole. However, if you were in Maine, where the declination line 19° , the magnetic needle would point 19° to the west of the True North Pole.
Maps and direction are usually based on True North and it is usually desirable to have your compass read True North. When this is done, the needle will point to the True North reading on the graduated compass circle.
Compass circle adjustment for declination is easily accomplished by rotating the compass graduated circle with the slotted screw that extends through the side of the case. The declination angle for you are can be determined by the isogonic chart (Fig. 2) or from the marginal notes of topographic maps. The following paragraphs explain the declination adjustment (note the declination angle referenced by date on map).
When the Magnetic Declination is Zero
With the compass circle adjusted for zero declination, the zero of the compass circle should be directly under the zero index in. If it is not, turn the slotted screw until the compass circle is rotated to the correct position. In this position the compass reads magnetic bearings (see Fig. 3A).
When the Magnetic Declination is East
To adjust for east declination, rotate the compass circle clockwise from the zero pin the number of degrees of declination. For example, 15 degrees east declination is adjusted by turning the slotted adjustment screw so that the compass circle rotates clockwise from the zero pin 15° . 15° should then be located directly below the zero pin (Fig. 3B).
When the Magnetic Declination is West
To adjust for west declination, rotate the compass circle counter-clockwise from the zero pin the number of degrees of declination. For example, 15 degrees west declination is adjusted by turning the slotted adjustment screw so that the compass circle rotates counter-clockwise from the zero pin 15° . 345° should then be located directly below the zero pin as 360-15=345 (Fig. 3C).
Before the compass is used, the compass circle should always be adjusted for the magnetic declination of your area. For current declination information contact The Brunton Company (latitude and longitude are required).
A bearing is the degree reading or direction from your position to another object. Thus, if you were in the field and a mountain peak was directly east of your position, the bearing of the mountain would be 90° . If the peak were directly to the south of you, its bearing would be 180° , and if it were to the west of your position, the bearing would be 270° (This assumes a 0° to 360° graduated dial). The term azimuth is sometimes used instead of bearing.
The instrument is held waist high and the lid is opened toward the operator at about 45° (fig. 4). The front sight is set perpendicular to the bottom case. The instrument is held flat in the left hand with the mirror next to the operator. The left forearm is against the waist and the instrument is steadied with the right hand. The instrument is correctly sighted on the object when the user, while looking down into the mirror, sees the black center line of the mirror bisecting both the front sight and the object sighted. At this point, the bubble is the circular level vial is centered. The North seeking end of the needle then points to the bearing angle on the compass circle that the compass is pointed. Caution: The compass reading cam be affected by magnetic materials such as watches, belt buckles, knives, cigarette lighters, etc. All magnetic material must be kept away from the compass when readings are taken.
Suppose you know what the bearing or degrees to an object is. The object may be a town, a mountain, a lake, or some other place you wish to travel. The bearing may have been given to you by instruction or you could have obtained it from a map. With the bearing known, it is a simple matter of finding your line of travel to the object.
The instrument is held waist high as explained above and shown in figure 4. With the compass held horizontal so that the magnetic needle is free to rotate, pivot yourself and you compass around until the North seeking end of the needle points to the desired bearing on the compass graduated circle. The compass will now be pointed in the correct direction. Your line of travel to the object is now an imaginary line extending straight out from the large sight.
For walking long distances, it is best to select a tree, rock, or some object easily seen in you line of travel , and then walk to that object. After reaching that object, use your compass again to determine you line of travel and select another object to walk toward.
When greater sighting accuracy is required, of where the bject sighted is far away, it is generally better to use this method (fig. 5).
In cases such as this, set the front sight vertically of slightly sway from the body case. Turn the tip of the front sight up. Holding the instrument in both hands at eye level (with the front sight toward you), sight through the front sight and over the mirror or through the window in the mirror at the object, The mirror in the cover should be angled so the compass needle and compass circle cam be seen in the mirror, Centering of the round level cam be accomplished at the same time y observing it in the mirror. With the compass sighted on the object, the black end of the needle points to the bearing angle, and can be read in the mirror. The black end of the needle is used instead of the white, north-seeking end, since the sighting direction of the compass is reversed with this method of sighting.
Your Brunton compass is also capable of measuring vertical angles to accuracies of better than 1° . Referring back to figure 1, the parts of the instrument used tin vertical angle measurements are the long level, vernier for vertical angles and the vernier lever on the bottom of the compass case (not shown in fig. 1). The lever on the back of the case is attached to the long level and vernier. By rotating the lever, the long level and vernier also rotate.
On the inside bottom of the compass, above and below the vernier, are two scales. The scale below the vernier is graduated from 0° to 90° for measuring vertical angles in degrees. The scale above the vernier is graduated from 0% to 100% and measures vertical angles in percentage of grade. This scale cam be used to determine the height of an object and will be explained later.
Suppose you are out in the field and wish to obtain the vertical angle from you to the top of a tree (fig. 6). To measure this angle, rotate the front sight all the way open, turning