Abstract: A visual teaching aid adapted for teaching groups of students in a classroom environment how to read rules and understand dimensional relationships. The teaching aid includes a relatively large sized elongated board adapted for horizontal wall mounting. The board has a scale along the length thereof depicting known units of length proportionally larger than the actual units and a selectively positionable pointer carried in depending fashion from a slide track mounted along the top of the board. A draw cord arrangement, which is operable from either end of the board, is adapted for moving the slide in the track to selectively position the pointer at desired locations along the scale.