One of my most important props is a wooden stick made according to the specifications recommended by Tommy Kono. It has grooves which mark a 34" and a 38" wide grip and a mark for the middle of the dowel/broomstick. Especially the latter tells volumes when you do dislocates infront of a mirror. I never realised that my dislocates were asymmetrical ( 1--2cm) before I used this stick. As you can feel the grooves slippage of grip is greatly reduced via feedback.
Well I got a lot better at dislocates in a short time and will add 30" and 26" marks soon...