180 Degree Rule

The 180 Degree rule is a simple guidline that states that two charaters in the same scene should always have the same left/right relationship to each other. In this technique you cannot pass the invisible axis or this will be called crossing the line.

This is an example of the 180 degree rule.
On the right of the picture is showing how the 180 degree
rule is suppose to be used. The on the right it a shows an example
of what crossing the line is. So when the camera cuts across
the line the characters switch places.

I also have a video which would be useful for understanding it fully in the link below.

http://www.youtube.com/watch?v=BBPw9C57TuU