Where the rocker meets the floor with the seat level, measured forward from the rear edge of the seat. The legs are cut wherever they meet the circle.
How far the seat runs on behind where the back meets it. The contact point is measured from that rear edge.
The angle the back makes with the floor once the chair settles under the sitter. Type a target and the contact point moves to give it.
The shins keep their length: a low seat lifts the knees and puts more weight on the feet, which pitches the chair back.
Level is the layout view, seat parallel to the floor. At rest lets the chair settle to its natural tilt. Rock gives it a push.