AOFAR AF-4074 Military Compass

1. Components Name

The AOFAR AF-4074 Military Compass features the following components:

• 1. Lid
• 2. Reading Lens or Prism
• 3. Window with Aiming line
• 4. Hinge
• 5. Scale (Centimeter Ruler on opposite side)
• 6. Tripod Connection
• 7. Spirit level
• 8. Glow-in-the Dark Arrow No1
• 9. 360° Rotating Bezel Ring
• 10. Glow-in-the Dark Arrow No2
• 11. Clinometer
• 12. Glow-in-the Dark Circle (Fixed tip point)
• 13. 360° Compass Card (Thermoelastic Liquid-Filled Capsule with Floating Dial)
• 14. Holding Ring
• 15. Aiming Point
• 16. Sighting Lens with Adjustable Diopter
• 17. Heavy-duty zinc Die-Cast
• 18. Conversion chart: Angle/Gradient/Distance
• 19. Distance-measuring notches

2. Product Specification

The compass consists of a Zinc alloy housing and a metal lid with a glass window etched with an aiming line. The window is mounted in the lid with a robust hinge that can be turned through 180°, allowing it to be moved into reading position and folded back after use. The compass is equipped with a clinometer for measuring slopes and gradients in degrees or percent, and an integrated spirit level. It can be screwed onto a tripod for simple terrain surveys. The sighting lens system, with an integrated index line and magnifier, allows for precise readings, eliminating parallax errors through prismatic reading. The dial system's damping ensures rapid and accurate readings.

3. Use Tips

To use the compass, adjust the lid up or down until the Aiming Point, aiming line, and the object are aligned. Ensure the compass is held horizontally using the integrated spirit level. By skillfully handling the compass, align the aiming line with the aiming point, ensuring your eyes, the compass dial, and the object are at the same level for utmost accuracy. This method allows reading fractions of an angular degree. Adjust the prism or lens position on the 360° Rotating Bezel Ring until the numbers on the compass card are clearly visible. For models with an adjustable eyepiece, rotate the Sighting Lens until the degree numbers are visible. For optimal results, hold the compass 1-2cm from your eyes.

4. How to Define the Value of Marching Direction

With the compass in reading position, aim at an object through the Aiming Point and aiming line. Read the marching direction value on the compass card, which corresponds to the object's azimuth.

5. How to Follow the Value of the Marching Direction You Defined

If the marching direction value is known, consult the compass card and turn until the specified value appears on the graduated dial.

6. Map Orientation

For complex operations on a topographic map, orientate the map's geographic north with the Earth's magnetic north. Place the compass on the map, aligning the centimeter-marked line with the nearest meridian, so the upper lid points to the map's north. Hold the compass in position and rotate the map until the north-seeking needle coincides with the index line of the Glow-in-the Dark Circle. The map is now oriented with the ground.

7. Let's Define the Marching Direction on the Map

1. After aligning the map with the north pole, draw a line on the map from your position to your final destination.
2. Place the compass on the map with one edge along this line. The compass lid indicates the direction of the objective.
3. Read the marching direction value on the compass card, corresponding to the index line of the Glow-in-the Dark Circle.
4. Remove the compass from the map, consult the compass card, and turn until the defined marching direction value appears.
5. Find an auxiliary destination point on the same survey line and start following it.
6. Repeat this process until the final destination is reached.

The longer the route, the more frequently this operation needs to be repeated to maintain the defined direction.

8. Let's Define Our Position on the Map

Select two visible points on the ground and mark them on the map. Once the map is oriented (as per Point 6), use the compass to measure the position value in degrees (A) and draw a line on the map accordingly. Then, proceed through point (B).

9. Let's Use the Clinometer

The clinometer measures differences in height and slopes and can be pendular or automatic. Open the compass and adjust the Clinometer until it is perpendicular to the case. Aim at the upper or inferior edge of your target using the Aiming line. Ensure a single line is formed. Tilting the compass changes the clinometer's position. Aim at the target and tilt the compass on the clinometer side until the pendulum stops, then read the angle of inclination. If the object is below the observer, turn the compass so the hinge points towards you, aim through the upper part of the lid, and follow the instructions.

Example: If the first degree value is 4 and the second is 354, the angle is 10 (360-354+4=10).

Table 2: Conversion Chart

10. How to Estimate the Distance to the Object by the Map

Measure the distance to the object on the map using the Centimeter Ruler (5) and multiply by the map's scale.

Map Scan: 1:25000
Distance(M) = Distance (mm) on the map X 25000 / 1000

Map Scan: 1:50000
Distance(M) = Distance (mm) on the map X 50000 / 1000

11. The Height of an Object

You can measure or estimate the distance to the object on the map as described in Point 10. Multiply this distance by the factor indicated in column IV or V of Table 2, referring to the angle measured with the clinometer (Point 9).

Example: An object is at a distance of 2000m, and the measured angle is 14°. Using column IV (25%) or column V (1/4) from Table 2, the height is calculated as:

2000m X 25% = 500m

OR 2000m X 1/4 = 500m

12. How to Measure the Angle

Measure the angle on the right side of the object. Keeping the first value in mind, slowly orientate the compass towards the left side of the object. Deduct the second value from the first to find the angle between the left and right sides of the object.

Note: When measuring the angle through the north, if the value 360° (north) aligns with the direct line on the Glow-in-the Dark Circle during measurement, consider 360°=0°. The calculation will be 360° - second value + first value.

13. How to Measure the Distance on the Ground

Using the principles from points 10, 11, and 12, you can determine the ground distance between two visible points. This can be used to measure the width of a building or the length of a bridge. A key condition is that the line from your position to the object must be as perpendicular as possible to the object's side being measured.

Example: A bridge spans a river at a distance of 4000m. If an angle of 6° is measured from the right to the left river bank, the bridge length is calculated as:

6° = 10% or 1/10

4000m X 10% = 400m OR 4000m X 1/10 = 400m

14. Measure of the Distance of an Object, the Height and/or Width of Which Are Known

If the height or width of an object is known or indicated on a map, its distance can be found by inverting the calculation described in Point 13. For instance, if the width of an object corresponds to 1/7 of the distance (Table 2), the distance is 7 times the width or height.

Example 1: A TV tower is 200m high. The measured angle is 7° from bottom to top. Column IV (gradient %) indicates 12% for 7°.

100% X 200m (height of object) / 12% (column IV, Table 2) = 1600m

OR 200m X 8 (inversion of 1/8) = 1600m

Example 2: The angle measured between objects B and C is 34°. The distance between B and C is 5 km. Column IV, Table 2 indicates 66%.

100% X 5km / 66% = 7.5km OR 5km X 3/2 = 7.5km

For this method, the object of known width must be perpendicular to the line of sight.

15. Measure the Distance with Scale-Marked Glass

The glass cover has aiming lines and measuring notches. These notches allow distance measurement when the distance between the target and another visible object on the same level is known.

10 notches = 0.9cm. Each notch = 1/9cm. The distance between eyes and the aiming line is 12cm.

Example: If the distance between two objects is 36m and the notches on the glass are 12:

(12CM / 0.09cm) X (12 / 2) = 400m

400m is the distance between you and the object.

The simple formula is: (1200 X 36m) / (9 X 12) = 400m

If the distance between two objects is 36m, the notches on the glass are 12, and for another object at the same level, the notch is 18, the distance is 36/12*18 = 54m.

16. Warning!

The oscillation of the needle in a high-quality compass is stabilized by the liquid it is dipped in. Variations in temperature or pressure can cause small air bubbles around the compass card, which do not affect functioning and disappear within 24-48 hours under normal temperature conditions. Avoid using the compass at temperatures below 0°C. Stay clear of magnetic fields from iron parts, magnetic cores, or electric wires, as these can cause inaccurate readings. Prevent the instrument from falling or damage, and do not tamper with it to maintain the warranty.

17. Contact Us

Email: service@aofar.com

URL: www.aofar.com