An early mechanical calculator whose design has evolved through the centuries, with two styles in use today. Both the Chinese and the Japanese styles consist of a frame with a crossbeam. They may be made from many different materials, such as wood or brass. Rods or wires carrying sliding beads extend vertically through the crossbeam. The Chinese suan pan has two beads above the beam on each rod and five beads below. Each rod of the Japanese soroban carries one bead above and four below. Similar to the abacus in both construction and use, but much larger, are the counting frames used in elementary schools. Braille versions of the abacus are available for use by those without sight.