Using the face of a clock is a common way to illustrate casting but it is also very misleading for the beginner.
The two major ways the angler moves the rod is by rotation of the rod butt and by the stroke path. Lets define what those are. Rod butt rotation is what the clock face is. If we say 10 to 2, that is 4 hours or 1/3 of the 360 degrees of the clock face or 120 degrees of rod butt rotation. Way too much in my opinion for a beginner cast. Since beginners tend to have poor stops and floppy wrists, that 120 degrees become 160 or 180 and we get the windshield wiper cast.
The other factor is the stroke path. That is the movement of the rod butt handle through space. Rather than just rotating the rod around the butt cap, the rod can move back and forth, up and down, right and left. Whereas the rod butt rotation occurs in a two dimensional space with the base of a rod fixed at a point, the stroke path is the movement of the rod through a 3 dimensional space.
To illustrate the difference, look at the video at the Sexy Loops that uses a rod with the rod butt fixed to a table top. The rod is like a flexible clock hand rotating on a clock face. This is exactly the image we give to novice casters. But notice that when the rod butt is fixed, because of the shortening of the chord length of the fly rod as is flexes, every cast MUST be a tailing loop.
One of the purposes of the stroke path is to move the rod in a convex path, to correct of the concave path of the rod tip as the the rod shortens due to its flex.
Why does the stroke of the rod naturally go in a convex path. Fortunately the joints we use to cast with naturally move the hand in a convex path. We cast with the shoulder, elbow, wrist, and sometimes with body rotation. Allow you arm to hang down loose and swing it - the hand swings in a convex arc. Bend your arm at the elbow and do a karate chop - your hand goes in a convex arc. Extend your fingers and flex your wrist in any direction - your finger tips go in an arc. Stick your arms out to the sides lie helicopter blades and rotate your body - your hand go in a convex arc. In fact, almost every hitting sport like tennis, golf, baseball moves the arms in an arc and so does throwing a baseball. So convex movements are natural and concave are unnatural.
The problem with the clock face is that 10 - 2 (120 degrees) or even 10 - 1 (90 degrees) is too great a rod butt rotation. I once read a study on the optimum amount of rod butt rotation for a beginners cast and if I recall correctly it was well under 90 degrees. Since beginners tend to overdo the rod butt rotation, I use 10 -12 or (60 degrees). In fact, both Gary and Jason Borger have beginners pantomime by stopping the "rod" on their foreheads do they cannot go too far. This is to emphasize the stop point for the back cast.
Here is Jason Borger demonstrating the stop for the backcast:
Here's Gary's audience at this year's Pasadena fly fishing show as he demonstrates the basic cast stop point. It is not the "L" for losers
but the firm stop for a winning fly cast.
So teaching rod butt rotation is "but" one part of the cast. The other is to teach a easily learned foundation stroke that will move the fly rod in an convex path to compensate for the fly rod shortening. That is for another time.