It is a fractional ball perception, or initial ballpark positioning of the vision relative to the cue ball and object ball orientation to the pocket, and then adjusting that vision in the 3rd plane (height and distance from the cue ball to the eyes) to those relative positions. This 3rd angle projection (which is really a very complex compound angle relative to cue ball and object ball centers) can be mathematically explained with the implementing of a few kinematic equations. But that may confuse people since the variables for those equations would always differ on every shot, so Stan, with his level of dedication, has over the years contrived no less than 4 different ways of explaining to people how to get their vision adjusted close enough to make most shots without adjusting their aim after addressing the object ball. Without that adjustment to vision after the perception and before cue ball address, all 1/2 ball hits would cut at 29 degrees. Simplified, with 2d fractional ball aiming the only variable is the diameter of the balls, since nothing else changes the angle. But with the addition of the 3rd or 3d perspective applied, then many more variables apply, even now the distance between the balls, and distance from the balls to the pocket matter as variables which can perfectly define exactly where the vision center needs to be placed relative to every shot with the application of kinematic formulas, which are used in pretty much anything engineered to achieve and objective relative to motion. These variable are why a 1/2 ball hit on 1 pair of balls cuts say 26 degrees and yet the same 1/2 ball hit on 2 other balls positioned differently on the table would be cut maybe 34 degrees, and so on. It's just math, but it's not just simple math as used to define basic fractional aiming. But, again, to simplify things, Stan explained at least 4 other ways to do it close enough. I think he did good.