It's amazing how often certain shot angles come up. Like with fractions, for example, halfball hits are very common. Depending on how far the ob is from the pocket, a halfball hit could work anytime the shot angle is between about 25° to 35°. This wide range (10° window) is of course only when the ob is within 12" of the pocket. From 2 diamonds out the range narrows to about 28 to 32 degrees, a 5° window. And from half table it's about a 2.5° window, or about 29 to 31 degrees.
Regardless of the fact that all pool shots fall anywhere between a 0° and a 90° cut, when we consider the margin of error at the pocket we can drastically reduce the amount of shot/aiming possiblities. In other words, we rarely have to be exactly dead on. Fractionally, with an ob about a diamond from the pocket, the aim can be narrowed down to 1 of 4 aiming options, thinning or thickening the chosen aim line a touch if needed. From 2 diamonds we have about 8 options. And from half table we can narrow it down to 1 of 16 options, thinning or thickening the chosen aim a touch here or there as needed.
My point is....we very rarely (if ever) have to choose that exact 1 out of 90 degree aim. Usually we're playing within a window of a handful of shot angles, thinning or thickening as needed based on experience. If you work with any system long enough that gets you very close to the shot line, then eventually your brain (through experience) will begin to finalize or tune into the final aim quite accurately. It doesn't matter if you're finalizing with a pivot, a sweep, a little spin, or simply aiming to hit the ob a quarter or eighth of tip thinner or thicker. The more you do it the better you get at it.