An abacus is the earliest and most simple form of a calculator. All the arithmetical processes can be carried out on an abacus. This is done by changing the position of beads on counters.
The most common type of abacus is a small rectangular frame with several fixed verticle rods. Beads or counters are on these rods. They are then able to slide up or down.
Each of the rods represents a decimal place. In a simple abacus (one rod only), each bead has the value of a single decimal place.
Addition is done by moving beads together. Subtraction is done by moving beads away from other beads.
The abacus can also be used for multiplication, division, and finding square roots.
The origin of the abacus is unknown. It may have developed from the use of notched sticks and stones.
The earliest abacus was most likely a dust covered tray. Tally marks could be drawn in the dust and swept away with the hand.
The problem with using an abacus is that a record of the arithmetic process is not kept. If a mistake is made, it is impossible to know where it was made.
For those who are skilled in using an abacus, it is still the best tool for arithmetic processes other than multiplication.
As written number systems developed, the abacus fell out of use.
Today, the abacus is primarily seen as a teaching tool for Kindergarten. This is mostly true in the Western world. In the Eastern world, the abacus is still a tool not only of education, but for tradesmen, business men, and race-track cashiers.
No matter how the abacus is used, it holds an important technological place in history.