OMG Rick! "Erect contrived road blocks" Are you serious? LOL How can you be so obtuse? Ok...here's a "polite clarification" for you...a pendulum swing works from the elbow down. It does not engage the shoulder at all. It has a measurable, linear, nonrandom range of motion, that's specific to each individual. With that said, the elbow is a hinge, so it physically has to open and close in a straight line (wrist twisting notwithstanding). Things like grip placement, tension, and timing all play a role in how straight that line is, and the personal shooting template determines the other variables, including but not limited to, stance, eye positions and patterns, bridges and PSR's. All of these things contribute to developing and maintaining an accurate and repeatable stroke, especially under pressure. For many players, of all abilities, who struggle with consistency, if there is any shortcut to a good stroke, an SPF stroke is a good choice.
A piston stroke utilizes the shoulder, which is a ball and socket, and uses four muscles (vs. one/biceps) to deliver the cue. A piston stroke may or may not be a straight line. A pendulum stroke is a straight line, using the pinned elbow technique. A piston stroke has essentially the same beginning (tip to hand), but no repeatable finish position, making timing much more prone to small error. A pendulum stroke has the same beginning and end for the majority of SOP strokes (Standard Operating Process = Autopilot). That will cover 90%+ of all shot situations. That makes it easier to learn, takes less time to master, and once you really learn it, you never forget how to do it correctly (caveat: everyone has their own personal "correct").
Since tip contact is extraordinarily short (1/1000th of a second, or 1/4 of an eye blink), the only time the cue needs to be as level as reasonable for the shot, is at contact with the CB. Pendulum, piston or some other variation...all that matters is tip contact. Pick your way to deliver the cue...and practice. Since we're not deriding the piston stroke...just stating factually that it is, in the end, a choice, nonetheless more difficult to learn, repeat and master, than a pendulum stroke...you'd think you'd actually be bright enough to just let it go. Like Randy & Jerry said: There are two types of students...those who want to learn; and those that want to prove you wrong. You're simply the latter.
Scott Lee
http://poolknowledge.com