Borger's drawing isn't what most people visualize when you tell them to "go from 10 to 2" though. Beginners hear that and they will invariably lock their arms in place and rotate their wrists from a fixed point in the "center of the clock". But Borger is sending the rod up and back (by moving from the shoulder) in the back cast and then down and forward in the forward cast. The drawing is a little misleading too, because it shows the rod tip positions at the back cast and the end of the forward cast to be on the same level while the rod butts are not. The lines representing the rod are different lengths in his drawing, but of course an actual fly rod doesn't change length. If your hand is higher up in the back cast than it is in the forward cast, then the rod tip will be higher in the back cast as well.
The rod tip and the line will not travel a level path in the back cast with that stroke (as implied by the level lines on the drawing). The line will go up as it goes back. Then the rod and the line will drop and go forward. That allows the rod end of the line to travel underneath the leader end of the line in the loop (avoiding a tailing loop), and as long as you don't drop the rod too much in the the forward cast, you'll get a nice tight loop going forward.
The biggest difference between Borger's drawing and the FFF photo is in the arm movement. Borger illustrates moving from the shoulder, allowing the arm to travel up and back and then down and forward (same as Chris's drawings pretty much). The FFF photo shows the guy's upper arm locked, and he is bending from the elbow (and a little wrist) only. That photo is a little closer to what a lot of people visualize when they hear "10-2". You can see that his rod tip is moving in more of an arc - low in the back, high in the middle, and low in the front. Also, the loop going forward is bordering on the large side. That works OK for me on shorter casts, but I get tailing loops and/or big open loops if I try that with medium to longer casts.
If you watch Jason Borger in "A River Runs Through It" and look at the photos in the post above, you see him moving his entire arm - up and back....then down and forward. He doesn't lock his arm and rotate around his wrist or his elbow. If he did, his casts would suck.
As far as the semantics goes, "10-2" descriptions appear to communicate the right things to some folks, but a lot of people visualize an improper technique when they hear those words. It does appear that everybody pretty much agrees on what proper technique looks like. There are just different opinions on how to best describe it verbally.
If you REALLY want a verbal exercise, try to describe this casting technique with words only: Advanced Trick Casting: The Shadow Cast - YouTube
---------- Post added at 07:34 PM ---------- Previous post was at 07:10 PM ----------
Here's a video that showed up on the side of the page with the one I just posted. This one is Steve Rajeff talking about the cast. Although he mentions "10-1" (not 10-2), the rest of his description and demonstration shows him moving his entire arm up and back and then down and forward, with more exaggerated movements of both his arm and his body on longer casts.