© Islington Artefact Library

The abacus has been used by the inhabitants of China, Japan and Russia for thousands of years. It is the ancestor of our modern calculator although not as we know it. The users of an abacus would carry out the calculations in their head, and would use the abacus to keep track of the sums and carryovers as necessary.
The invention of the abacus evolved from a simple need to count numbers. Merchants trading goods not only needed a way to count goods bought and sold, but also to quickly calculate the cost of multiples of those goods. Until numbers were invented these counting devices were used to make everyday calculations.
The earliest abacuses have been lost in time due to the perishable materials used to construct them. However, we know that the simplest abacuses probably involved drawing lines (representing units, tens, hundreds etc.) in the sand using small pebbles as place holders representing numbers within those marks. With the need for something more durable, wooden boards with grooves carved into them were created. The oldest surviving counting board is the Salamis tablet which was used by the Babylonians in about 300BC.
During the Middle Ages wood was the primary material from which abacuses were manufactured. As HinduArabic number notation gained popularity in the latter part of the middle ages, particularly with the advent of notation for zero, the use of the abacus began to diminish in Europe. However, the abacus is still used in the Middle East, China and Japan. Many competitions have been held in order to tell which method is quicker when completing a complicated calculation. A man skilled with an abacus is likely to beat a man noting his calculations with a pencil and paper!
The abacus in the picture is divided into two decks by a crossbar. It is held horizontally with the smaller deck at the top. Each bead on the top deck has the value 5 and each bead on the lower deck has the value 1. The beads are pushed towards the central crossbar to show numbers. Working from right to left, the first vertical line represents units, the next tens, the next hundreds and so on. So for example to show the number 9, on the first line, one bead from the top deck would be moved down (representing 5 units) and 4 beads from the bottom deck would be moved up (each representing 4 units). To show the number 79, in addition to the beads in the first line used to make the number 9, one bead would be moved down on the upper deck and two beads from the lower deck would be moved up on the second line, representing 5 tens and 2 tens respectively.
