To perform art of visual ballistic ( determine where ball gonna stop with probability higher then random), we need to identify particular moment into the spin , wich will become our prediction moment.
A bit of physics. .. when ball is launched it has impulse ( potential energy) on its maximum. Slowly it will convert this energy to kinetic ( energy of the moviment). While potential energy is on its high, ball tend to rotate on upper ball track. Ball has negative acceleration. It simply means that due to the friction and air resistance ball will loose it's speed gradually.
Initial rotations of the ball do have very low deceleration due to the high momentum that ball posses. If you take timings of rotations of the ball, you will see that initial revolutions of the ball do have very little difference in time.
It's not so when ball starts to slow down on posterior revolutions.... time differences between rotations of the ball start to grow.
When we can reliable way to destinguish between rotations to pin point one specific between them , we may start to speak about prediction.
Rotation timings are relatively "consystent".
Why relatively and why ("")? Simply because timings of rotations do depend on some external factors including additional spin axis wich ball may have ( due to dealers type of throw), atmospheric pressure...ets.
But for explanation purposes we will consider them consistent.
Traditional vb focuses on specific revolution of the ball identification. So wich revolution to choose for prediction moment?
There gonna be one particular moment into the spin, when revolution timing will be considerably different from others. It will happen due to the fact that ball already lost much of its initial impulse ( converted for energy of moviment).
Warning... it's most visible on older type of wheels where separation for lower and higher ball track does exist.
So.. ball lost its momentum,it starts to exit higher part of ball track and tougch lower part of ball track. On the moment this phenomena happens ball gain aditional friction point. Now it tougch ball track in 2 places instead of 1. It will be a reason for a ball to have higher decceleration ( loose more speed per revolution).
This moment is called " knee point", because if you make a graphic of decceleration in time , you will see line being broken in one place. There are many of these graphs on google so long do not gonna bother to post one here.
This " knee point " can be easy identified by both visual observation and distinctive sound that ball makes( on situable wheels).
Later l wIll continue on the topic... if someone wish to add something , you are welcome.