Abacus

An abacus has beads that slide on rods. It can be used to count, add, subtract, multiply and more.

The most common abacus is split into two basic rows: There are two beads in the top row, and five beads in the bottom one.
 * the top row for the "5"s, and
 * the bottom row for the "ones".

For example, 7 can be made by using one bead on the top row, and 2 beads from the bottom row, because 5 + 2 = 7

Have a play with this one:

Every column represents a different digit, such as Units, Tens, Hundreds, etc.

The abacus has been around for thousands of years, and is still used in some parts of the world. Sometimes blind people will use an abacus, because they can feel the numbers easily.

Expert abacus users can sometimes do calculations faster than on a calculator, and can even use them to find the square root of whole numbers.

https://www.mathsisfun.com/numbers/abacus.html