The 30-DEGREE RULE states that if an editor cuts to the same character or object in another shot, the second shot must be positioned at least 30 degrees away from the first camera setup.
If the camera moves less than 30 degrees, the cut between shots can look like a JUMP CUT or a mistake. A jump cut happens when two shots are cut together, but the camera position doesn’t change much but the subject moves in the second shot (jumping around the frame), giving the impression that time has moved forward. This type of cut can be very jarring to the audience, making them notice the technical side of filmmaking instead of being focused on the story.
There is no guarantee that slavishly complying with the 30-degree rule will save you from the big bad jump cut. In spite of their common subject and shot scale, and despite shifting the viewing axis by more 30 degrees, this couple of shots simply don’t fit together. It just feels weird. So clearly, the 30-degree rule is not bulletproof, and a good rule of thumb might be: You never know until you try. So try, and simply discard the result if it doesn’t work and try a different combination of shots (like using a different shot scale, inserting another shot (i.e. an insert) in-between, or using an establishing shot or a moving shot instead).
Example: 30 degree rule