Editing Abacus (section)

==Visually impaired users==
An adapted abacus, invented by Tim Cranmer, and called a Cranmer abacus is commonly used by visually impaired users. A piece of soft fabric or rubber is placed behind the beads, keeping them in place while the users manipulate them. The device is then used to perform the mathematical functions of multiplication, division, addition, subtraction, square root, and cube root.<ref name="aph">{{harvnb|Terlau|Gissoni|2005}}</ref>

Although blind students have benefited from talking calculators, the abacus is often taught to these students in early grades.<ref>{{harvnb|Presley|D'Andrea|2009}}</ref> Blind students can also complete mathematical assignments using a braille-writer and [[Nemeth Braille|Nemeth code]] (a type of braille code for mathematics) but large multiplication and [[long division]] problems are tedious. The abacus gives these students a tool to compute mathematical problems that equals the speed and mathematical knowledge required by their sighted peers using pencil and paper. Many blind people find this number machine a useful tool throughout life.<ref name="aph" />