Shun Chan is a term used to represent natural twining when that twining moves inward towards the center of the body. For the right hand the whole-body spiraling is a clockwise rotation and for left hand leading the direction is counter-clockwise. In either case the little finger leads the direction of the rotation. The feeling is one of scooping, as if scooping water, gently.
Ni Chan is a reverse twining or spiraling with the rotation going outward. For the right hand the rotation is counter-clockwise. For the left hand the ni chan is in a clockwise direction. In either case the thumb is leading and the leading is moving away from the center of the body.
Ni Chan and Sun Chan can be practiced as a “reeling-silk” exercise using the wrists alone with a focus simply on the turning of the hands. Little finger leading sun chan toward the body; thumb leading ni chan away from the body.
With practice the ni chan and sun chan can be felt in the practice of the forms.