Here is important to see and understand. The wooden rods just plug into the holes. Empty points remain very easy to recognize and clarify missing how much still to numbers printed. If one uses blue and red wooden rods, number decompositions, additions and subtractions are visible and understandable. Set of 10 plug-in boards (each 7 x 12 x 1.3 cm), 55 red and 55 blue wooden rods