Compass Structure
1. Direction Measurement Mechanism: Composed of a compass dial, a directional frame, a sight, and sight glass. The outer ring of the directional scale is divided in mils from 60–00, with units of 0–50 mils; the inner ring is a 360° division scale, with units of 5°. The directional indication accuracy is 0–25 mils.
2. Distance Estimator: Consists of a sight and sight glass. The sight glass is marked with distance estimation lines and mil scales. When the case cover and body distance positioning lines are aligned and the sight is in a vertical position, the distance fixing line and sight form a 10:1 ratio distance measuring device; the mil scale lines and sight form a mil-based distance estimator. The distance measurement accuracy is 5%.
3. Elevation Angle Measurement Mechanism: Comprises an elevation sight, an elevation pendulum, and a locking mechanism. Its range is ±90°, with units of 5°. The elevation angle measurement accuracy is 2.5°.
4. Mileage Measurement Mechanism: Made up of a mileage counter wheel, an odometer, an odometer pointer, and a gear system. The odometer has three scales: 1:100,000; 1:50,000; and 1:25,000, with units in kilometers. The mileage measurement accuracy is 2%.
5. Coordinate Ruler: Consists of two sets of measuring rulers perpendicular to each other. The long ruler is 80 mm; the short ruler is 20 mm. Unit is 1 mm. The coordinate ruler measurement accuracy is 0.5 mm.
Principle of the Compass
A compass uses the Earth’s magnetic field to indicate the north. It operates based on the principle that like magnetic poles repel and opposite poles attract. With north defined as the starting point at zero degrees, directions are determined clockwise. This allows for directional orientation. For accurate positioning, maps must be used to establish relative location and determine one’s current position.
Note that the north indicated by a compass is not true north but magnetic north. This is because the Earth’s geographic poles and magnetic poles do not coincide—they are offset by an angle called the magnetic declination. The magnetic declination varies from place to place and also changes over time at the same location.
Types of Compasses
The types of compasses commonly used for camping and hiking mainly fall into the following two categories:
1. Flat Type: Often rectangular, mostly made of transparent material. Due to their thinness, they are easy to carry in a pocket. Their transparent base plate and rotating bezel make them convenient to use on a map.
2. Box Type: Thicker in design, suitable for taking directional bearings by visual sighting, and is also commonly used by the military.
Precautions:
1. A good compass will have liquid injected into the rotating bezel to slow down the swinging of the magnetic needle, allowing it to stop quickly and point in a direction.
2. If you need to use the compass at night or in dark environments, you can choose one with luminous markings.
3. Generally, the white end of the needle points south, while the red or darker end points north.
4. The values on the bezel (degrees or mils) usually omit the last one or two zeros to save space (for example, 10 mils actually equals 1000 mils).
5. The orienting arrow always points to the 0-degree (or 0M) mark on the bezel, hence it is also called the compass north.
6. The direction-of-travel line must be aligned straight with the index line.
7. The above refers to the components of a flat-type compass, but not all compasses have all of these parts or functions.
Main Functions of a Compass
Determining Direction
1. Identifying the cardinal directions (east, south, west, north)
2. Orienting a map
3. Measuring magnetic azimuth
Measuring Distance
1. Measure map distances directly using a mapping ruler
2. Measure map distances using an odometer scale
3. Roughly determine the distance to a target at your location using a distance estimator
Calculation of marching time and speed
Using the speed-time table on the instrument, you can determine the required marching time while measuring the distance, or the marching speed within a set period. The method is as follows:
1. Marching time calculation
2. Marching speed calculation
Determine the slope angle (elevation/depression angle) of a slope
Open the instrument so that the mirror and the dial base form approximately a 45-degree angle. Hold the instrument sideways, aim along the sighting line and front sight toward the edge of the slope, keeping the sighting line parallel to the slope. Allow the angle measurer to swing freely, then check the scale reading indicated by the central line of the angle measurer in the mirror on the elevation/depression angle scale — this is the desired elevation/depression angle (slope). This function can be used to roughly measure the downward tilt angle of an antenna in wireless communication systems.
Measure the approximate height of a target
If the horizontal distance between the target (object) and your location is known, first determine the elevation angle of the target, then consult the height table to find out the target’s height.
How to use a compass
Use a compass to identify your current location:
1. Align the actual terrain with the direction on the map.
2. Identify two recognizable landmarks on the map.
3. Point the travel line (or long edge) of the compass toward one of the landmarks.
4. Align the circle with the arrow and the compass needle (north).
5. Without changing the orientation of the circle, place it at the north position on the map.
6. Align the tip of the long edge of the compass with the landmark on the map.
7. Draw a straight line extending from the circle’s arrow and the magnetic north line.
8. Repeat the same process for another landmark; the intersection of the two lines is your current location.
Use a compass to determine the direction of travel:
1. Align the straight line connecting your current location and your destination with the compass’s travel line (long edge).
2. Align the circle’s arrow and the magnetic north line parallel (with the arrow at the top part of the map).
3. Remove the compass from the map and hold it in front of your body.
4. Turn your body until the arrow and the compass needle overlap.
5. Then align the direction of the travel line — this equals the target direction on the map.
What are natural compasses?
During outdoor activities, a compass may be damaged or lost. In such cases, use certain natural features to determine direction, paying special attention to comprehensive analysis of specific situations.
Because the Earth orbits the sun and rotates in a counterclockwise direction, the sun rises in the east, reaches its highest point in the south at noon, and sets in the west in the evening. Note that due to the axial tilt of the Earth, daylight hours vary in different seasons, causing deviations in sunrise and sunset times.
1. The Sun
a. Stick a stick or straight branch into the ground, and draw a circle with the base of the stick (point O) as the center. At some time in the morning, mark the point (point A) where the shadow of the stick intersects the circle. In the afternoon, when the shadow again touches the circle, mark that point (point B). The line connecting these two points indicates the east-west direction. The midpoint of this line points south, while the opposite end points north.
b. Using a Watch Face and the Sun (Three Methods): Lay a watch with hands flat on the ground. Vertically place a small twig (or matchstick) at the tip of the hour hand. Rotate the watch so that the shadow of the twig overlaps with the hour hand, meaning the hour hand is pointing directly at the sun. The bisector of the angle between the hour hand and the number 12 on the watch face will indicate the direction of south.
Lay the watch flat and stand a small twig (or matchstick) upright at the center of the watch face. Rotate the watch until the shadow of the twig overlaps with the hour hand. The bisector of the angle between the hour hand and the number 12 on the watch face will then point north.
2. The Moon
The moon is Earth’s only natural satellite, and its brightness is reflected sunlight. As its position in the sky changes, the illuminated portion of the moon varies. We see the moon rise in the east and set in the west, displaying various shapes such as full, half, or crescent, known as “phases of the moon.” These lunar phases follow certain patterns in timing and direction, so knowing the phase and time allows you to determine direction.
3. Trees
It is commonly believed that tree branches and leaves are denser on the southern side and sparser on the northern side, or that the growth rings on the northern side are closer together while those on the southern side are wider. However, these methods are not always accurate because the growth of trees is influenced by many factors, including the environment, space, and sunlight.
4. Constellations
At night, besides the moon, you can also use constellations to determine direction. Finding the North Star is the most common method.
First, locate the Big Dipper constellation (also known as the Plough). It always maintains a fixed distance from the North Star as it rotates. Once you find the Big Dipper, extend the line connecting the two stars at the edge of the dipper (stars A and B) toward the direction of the dipper’s opening. Approximately five times the distance between stars A and B, you will find a relatively bright star — that is the North Star.
In regions south of 40 degrees north latitude, the Big Dipper often dips below the horizon, especially during winter evenings. In such cases, you should use the Cassiopeia constellation, which is opposite the Big Dipper, to locate the North Star. Cassiopeia consists of five stars with brightness similar to those of the Big Dipper, forming a “W” shape. The point located about twice the width of the gap in the middle of the “W” is where the North Star can be found.
In regions south of 23 degrees north latitude, the Southern Cross constellation can be used to determine direction in the first half of the year. The Southern Cross is made up of four bright stars forming a cross shape diagonally. Extending the line connecting stars A and B downward, the point approximately 4.5 times the distance between stars A and B marks true south.Pathfinder Donkey,OutdoorAdventureSelf-Driving Travel Network!For more comprehensive travel information, outdoor knowledge, experience, guides, and self-driving tips, visit the A Travel,Route Guides,Self-Driving ToursandOutdoor Adventure