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Abacus
An abacus is a counting device. Made of wood and string, or boards with grooves, or even board of sand and rocks. The abacus helped people to count, add and subtract numbers. This Roman abacus is a board with 4 horizontal grooves and 2 rows. The each top groove has 1 beads, each bottom groove has 4.
A typical abacus, that was used up until the invention of the calculator, has columns of string. It helps record place value. The abacus here is recording the number 4,213 with the position of 10 beads. Place value is very important, you can count up to nine on one column. Once you want to count to ten then you must move one bead on the next column and move the nine beads back to being in the 'uncounted' position.
This suanpan, or chinese abacus, can be used to count in decimal or hexadecimal A wooden abacus with 4 horizontal strings and 2 rows. The each top string has 2 beads, each bottom string has 5. The top strings are multiples of 5, the bottom string each bead means one, ten, hundred.
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