A quick little page on time keeping.

I was told how to determine how much daylight one has. While facing the sun, just hold up your fist with your arm fully extended. Your thumb should be laid on the top of your index finger, not crossing your palm. Position the top of your thumb to the bottom of sun, and count how many fists until you hit the horizon. Use your other fist to make up more space as needed. The number of fists you count is, roughly, the number of hours of daylight remaining.

On a solar equinox, the 2 days each year when there is equal daylight and night time, the sun travels 90º from noon to the horizon. 90º divided by 6 hours is 15º . The span of your fist approximates 15 from your eyes to the end of your arm. Thus your arm becomes a protractor for measuring the angle between the sun and the horizon. Because human bodies tend to be proportionate in the same ways, this method will work for most people. It does become less accurate the closer one is to either of the solstices.

Sundials

The 15º angle is also the basis for sundials. To make a basic sundial you must first know which way is true north. Magnetic north is is off of true north by several degrees. In a survival situation the loss of accuracy may not matter much. To determine true north with a compass you need to know the deviation for that locality. Some maps will include that information, however, it is not commonplace these days. Generally speaking the magnetic declination is about 5º. Determining true north is not difficult though. Use these 6 simple steps:

1) Push a rod into the ground. This can be any stick. You may want a stick that is very straight for a more refined sundial. Since we are using arm length as rule of thumb, select a stick that is bit longer than the distance from your elbow to wrist. That distance is approximately 5/12ths of the length of your arm and is a common length for a gnomon.
2) Use a pebble or a short piece of stick to mark the tip of the shadow.
3) Wait a period of time, 15 minutes or more will do.
4) Mark a second position after the tip of the shadow has moved.
5) Scribe a line from the first point to the second point. This line runs from West (the first mark) to East (the second mark)
6) True north is 90º from that line.

Another method uses an analog watch. A facsimile can be used if all you have is a digital timepiece. Aim the hour hand at the sun. Bisect the angle formed by the hour hand and 12 o'clock. The bisecting ray is parallel to the east - west line. Perpendicular to that, naturally, is the north - south line. Of course, using a watch this way begs the question why one would be constructing a sundial.

Using a straight rod, push it into the ground at an angle with the tip point true north. This is called the gnomon. If you make the radius of your dial the same as your arm length, then you can use your fist to mark out the hours. Plumb from the tip of your rod to your dial is noon. Every 15º to either side is an hour.