Safety / Survival / Army Field Manuals / AFM 3-05.70
Field-Expedient Direction Finding
18-1. The earth's relationship to the sun can help you to determine direction
on earth. The sun always rises in the east and sets in the west, but not exactly
due east or due west. There is also some seasonal variation. Shadows will move
in the opposite direction of the sun. In the Northern Hemisphere, they will move
from west to east, and will point north at noon. In the Southern Hemisphere,
shadows will indicate south at noon. With practice, you can use shadows to
determine both direction and time of day. The shadow methods used for direction
finding are the shadow-tip and watch methods.
18-2. In the first shadow-tip method, find a straight stick 1 meter (3 feet)
long, and a level spot free of brush on which the stick will cast a definite
shadow. This method is simple and accurate and consists of four steps:
Step 1. Place the stick or branch into the ground at a level spot
where it will cast a distinctive shadow. Mark the shadow's tip with a stone,
twig, or other means. This first shadow mark is always west—everywhere
Step 2. Wait 10 to 15 minutes until the shadow tip moves a few
centimeters. Mark the shadow tip's new position in the same way as the
first. This mark will represent East.
Step 3. Draw a straight line through the two marks to obtain an
approximate east-west line.
Step 4. Stand with the first mark (west) to your left and the
second mark to your right—you are now facing north. This fact is true everywhere
18-3. An alternate method is more accurate but requires more time. Set up
your shadow stick and mark the first shadow in the morning. Use a piece of
string to draw a clean arc through this mark and around the stick. At midday,
the shadow will shrink and disappear. In the afternoon, it will lengthen again
and at the point where it touches the arc, make a second mark. Draw a line
through the two marks to get an accurate east-west line (Figure
Figure 18-1. Shadow-Tip Method
THE WATCH METHOD
18-4. You can also determine direction using a common or analog watch—one
that has hands. The direction will be accurate if you are using true local time,
without any changes for daylight savings time. Remember, the further you are
from the equator, the more accurate this method will be. If you only have a
digital watch, draw a clock face on a circle of paper with the correct time on
it and use it to determine your direction at that time. You may also choose to
draw a clock face on the ground or lay your watch on the ground for a more
18-5. In the Northern Hemisphere, hold the watch horizontal and point the
hour hand at the sun. Bisect the angle between the hour hand and the 12-o'clock
mark to get the north-south line (Figure 18-2). If there
is any doubt as to which end of the line is north, remember that the sun rises
in the east, sets in the west, and is due south at noon. The sun is in the east
before noon and in the west after noon.
Figure 18-2. Watch Method
NOTE: If your watch is set on daylight savings time, use the midway
point between the hour hand and 1 o'clock to determine the north-south line.
18-6. In the Southern Hemisphere, point the watch's 12-o'clock mark toward
the sun; a midpoint halfway between 12 and the hour hand will give you the
north-south line (Figure 18-2).
18-7. Another method is called the 24-hour clock method. Take the local
military time and divide it by two. Imagine this result to now represent the
hour hand. In the Northern Hemisphere, point this resulting hour hand at the
sun, and the 12 will point north. For example, it is 1400 hours. Divide 1400 by
two and the answer is 700, which will represent the hour. Holding the watch
horizontal, point the 7 at the sun and 12 will point north. In the Southern
Hemisphere, point the 12 at the sun, and the resulting "hour" from the
division will point south.