What are some issues that can limit effectiveness of pivot-based aiming system?
The key to pivot-based systems appears to be the “pivot” and the effective center of the pivot. If you shift the bridge hand a small but critical amount during the pivot, then the resulting “line of aim” can be tweaked quite a bit. Assuming your initial alignment is consistent (for different but similar shots), and if you don’t adjust your bridge during the pivot, and if you don’t adjust by the exact right amount, you will miss many of the different, but similar, shots. As the diagrams in my articles show, the pivot-based systems will not work for a wide range of shots if the bridge is fixed during the “pivot” step (i.e., if the cue “pivots” about the bridge point), or if you don’t use different bridge lengths for different shots. In “Fundamentals – Part III: DAM aiming system” (BD, November, 2008), Diagram 1 shows how angle to the pocket matters, and Diagram 2 shows how distance to the OB matters. In “Fundamentals – Part IV: bridge length” (BD, December, 2008), Diagram 4 shows how bridge length matters with pivot-based systems. If a “basic cut-shot aiming system” does not account for the effects in these diagrams, then the aiming system will have limited use (without intuitive compensation). After numerous conversations over the years with many of the aiming system proponents out there, and after trying everything all of the proponents have suggested to me, it is not clear to me how the aiming systems account for the effects in the diagrams. If the systems work (and they seem to for many people), they must involve adjustments that account for these effects.
For more info, see the background information for the CTE aiming system, which is also an align-and-pivot system.