The Yellow Prisms for Volume introduces the concept of measuring the space inside a three-dimensional figure in a very visual way.  The set includes five yellow wooden prisms each measuring 20 cm x 10 cm x 2 cm, with markings to demonstrate how they can be divided into progressively smaller measurable units and then counted.  The prisms come in a special wooden box with one hinged panel to better comprehend the idea of volume. The box measures 22 cm x 13 cm.