Our goal is to change passive slump to active, upright sitting.
Watch the torso move into extension (taller).
The HipIndex will show the pelvis moving forward when upright and backward when slumping.
The exact angle of the indicator is not important, as long as there is some rotation movement of the pelvis.
The best way to find good spine posture is not by measuring an angle, but by feeling a small movement at the base of the spine.