What are the basics of the 90/90 pivot-based aiming system?
90/90 is an align-and-pivot aiming system developed by Ron Vitello.
Here’s a related document from Andrew Cleary containing some good illustrations.
As with all pivot-based aiming systems, there are issues that limit their effectiveness.
If you break the ball up into 10% increments, you want to line your cue up so that you are aligning the last 10% of the cue ball and object ball… or as Ron V calls, 90/90.
90/90 (pocketing without side spin/english)
Pivot your HIPS to the center of the cue ball. You should now be lined up to make the shot. If you pivot past center ball, don’t try to fix it while your down, just get up and start over.