Abacus 
The abacus is a mechanical aid used for counting. Addition, subtraction, division and multiplication can be performed on a standard abacus.
The abacus is typically constructed of various types of hardwoods and comes in varying sizes. The frame of the abacus has a series of vertical rods (at one time perhaps made of bamboo) on which a number of wooden beads are allowed to slide freely. A horizontal beam separates the frame into two sections, known as the upper deck and the lower deck.
Calculations are performed by placing the abacus flat on a table or one's lap and manipulating the beads with the fingers of one hand. Each bead in the upper deck has a value of five; each bead in the lower deck has a value of one.
Beads are considered counted, when moved towards the beam that separates the two
decks.
The rightmost column is the ones column; the next adjacent to the left is the tens column; the next adjacent to the left is the hundreds column, and so on. After 5 beads are counted in the lower deck, the result is "carried" to the upper deck; after both beads in the upper deck are counted, the result (10) is then carried to the leftmost adjacent column. Floating point calculations are performed by designating a space between 2 columns as the decimalpoint and all the rows to the right of that space represent fractional portions while all the rows to the left represent whole number digits.
