It is used to measure distance. You turn it on its side and roll it along a path on the map. This means it has to correspond to a particular map scale (my first guess is 1:50,000, but that looks a bit off). For a different scale you could do a simple conversion.
Can you tell me what the arc length of one major division is? From the picture, it kinda looks ...
Compass directions are, generally, always equally spaced around the circle.
The cardinal directions -- North, East, South, West -- are always 90 degrees apart.
If you know any one direction you should always be able to determine any other direction.
That said, there are some caveats.
Magnetic compass directions are actually under the influence of the local ...
A couple of additional items:
Angular units - Note that, for the full circle, it actually goes from 0 to 8. Each division is 1/8 of a circle. Each division is further divided into quarters, so the total number of subdivisions is 32, which is exactly how many points are in a compass. See
Distance measurement - It doesn't really matter ...
I agree with the other answer that one direction is enough to determine the others. As for actually doing it, it's very easy but can be confusing if your mind is overwhelmed by other things (e.g. if you are about to win or lose a race, or are very drunk).
I use the following rules:
If you are facing north, east is to your right, and west to your left
If you ...