What does it mean to sit correctly with one punch, one foot and one inch?

The distance from the chest to the table, the distance from the eyes to the book, and the distance from the finger to the pen tip.

1, one punch: keep your upper body upright, lean forward slightly, and punch your chest off the table.

2, one foot: the head is straight, naturally leaning forward, and the eyes are one foot away from the desktop.

3, one inch: when holding the pen, the upper body remains upright and can lean forward slightly. When holding the pen, the hand is one inch away from the nib.