I've been asked over time about why I don't do posts on the 1 plane swing theory. A lot of the theory I'm not a big fan of and I don't like how some of it is represented. However, it's always good to know what people are teaching and thinking.
So, here's the basic element of the 1 Plane Swing
This is a picture of Jose Maria Olazabal. As you can see, Olazabal's left arm is practically at the same angle as his shoulder plane (the angle of his shoulders). That's the major point of the '1 Plane Swing.'
That's opposed to what 1PS teachers call a '2 Plane Swing'
The idea is that a 2 plane swing will have to make the compensation of getting the left arm below the shoulders again to get the club on plane in the downswing. With the 1 plane swing, no compensation is necessary.
So, if you have some troubles with coming over the top, you may want to look at getting your left arm parallel to your shoulder plane at the top of the swing.