This app support Five and Half system only.

The frame point is where the ball is heading.
The rail point is where the ball touches.

Set the cue ball position.
Set the 3th cushion rail point.
The result is your 1th cushion frame point.

If the cue ball position is smaller than 50, the angle becomes narrower. If it is larger than 50, the angle is opened.

You can also calculate Plus system,
and Inside angle system(Short-Long-Short).