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With fractions, you need to estimate your subdivisions to determine where to aim. With contact geometry, you have a shot lattice keeping it true.
That goes along with my comparison of the three aiming methods and their references.
If someone learning with fractional aiming estimates a shot to be between a 3/4 and a 5/8 aim, they have a 7mm gap/subdivision to navigate within, which leaves them with three aiming options: Aim in the middle of the gap, aim slightly thicker than a 5/8, or aim slightly thinner than a 3/4. Using the tip/ferrule as a gauge is a good way to pinpoint the thinner or thicker aim lines, because an eighth of a tip is about 1.5mm. So the player must decide which of these options looks or feels right, and that is the aim line they use.
Every 1mm off will be about a 1° difference in the shot result. The more the player uses this method the more consistent they become with accurately estimating those in-between shots, shots that don't fall exactly on one of the eighth of a ball references. And it's rediculous just how often a shot actually falls dead in line on one of those references.
With ghostball, the learning player looks at the contact point line to the pocket and then estimates where the ghostball center is. Then they keep that spot in their mind or vision while standing behind the cb. From there they aim the cb to this spot. If they pinpointed the contact point accurately (which from directly behind the ob is fairly easy is to do), and they pinpointed the ghostball spot accurately, they have their aim line.
Every 1mm that they're off will cause about a 1° difference in the shot result.. This method also requires experience to become consistent with pinpointing that ghostball spot, but after enough experience the player will become more accurate and consistent with it.
With contact points, the learning player pinpoints the cp on the ob, then they keep that spot in their mind or vision while standing behind the cb. Then they either estimate what looks like an equal-opposite cb-ob overlap referencing the contact point, or they connect the dots (cb cp to ob cp), or they perform a parallel shift. If the player can do one of these methods consistently and accurately, then the entire aim line is based on that initial contact point reference.
Every 1mm that they're off on the contact point will cause a 2° difference in the shot result. With experience the player either gets very good at pinpointing that 0.5mm contact point, or they get more consistent at estimating the overlaps or the shifts needed to make it work.
Any of these methods can help a player develop consistent aiming skills, and it's really just matter of personal preference, deciding which method works best. Once you determine which method clicks for you, your road to developing solid aiming skills will be much shorter.