For the first time in the history of counting, in ancient times, people used pebbles or tied knots on ropes. Also, the easiest way to calculate was fingered. However, with the help of fingers, only a small number of things could be counted. The people of Greece and Egypt first started counting by drawing marks on the stone. In our country too, in ancient times, counting was done by drawing marks on the sand. As society improves, the need to compute increases, and various instruments are invented. The instruments that were available at this time were mainly hand operated. Then with the gradual change of time, these improvements happen and one unity calculator starts to be added to the history of calculation. Such as – abacus, Napier’s sister, difference engine …. etc

**Abacus**

It is a wooden frame with seven rods attached to each of the seven stones or pebbles. The rods were then divided by a horizontal rod, called a divider. The upper part of the divider was known as Heaven and the lower part was Earth. It had two bullets at the top and five at the bottom. These were easily counted up and down. The man of these depended on their position. It was invented in China around 3000 BC.

**Napier’s Bone**

In 1818, John Napier, a Scottish man, made a logarithm table by counting numbers on a few ivory rods. Each bar was divided into nine rectangular boxes. The angles in each box were again divided into two parts. The first bar contained numbers 1 to 9, and the latter contained multiples of these numbers. When writing multiplication numbers, the decimal number was written at the top of the box and the single number at the bottom. These bars could be easily arranged side by side

**Slide ruler**

In 1820, the English mathematician Slide Ruler named William Oughtred. It had two rulers. A ruler was fixed and the upper rule was counted up and down. In this, the functions of multiplication and division were done by addition and subtraction, respectively