I agree with David and Bob, cavity size is approximate, the sound of the call comes in the tuning stage. All the secrets of tuning are after this stage. I could list 20 factors after the routing stage. Old man Stribling used to let students from the High School in Rosedale turn out boxes and paddles ---- Then he would match them up and start tuning them. This must be a tool for low tech students that do not know how to drill a hole or where to put the hole!
It is a Turpin Style --- not the other fellow's style, He just copied Turpin.