180 degree rule

This is the 180 degree rule. The 180 degree rule suggests that once you start filming at one side of the line you cannot switch over to the other side of the line as the characters would switch positions. So if a character was on the left at the start of filming, and then the 180 degree line was crossed, the character that was once on the left of the screen would now be on the right of the screen. The 180 degree rule is usually used for when filming conversations.