Mental calculation or mental maths is an old mathematical tool. It is doing maths without using any tools or writing anything down. Mental calculation uses only the human brain. People who use mental maths use shortcuts to make the calculation easier. People who do mental calculation do it without a computer or a calculator. Mental calculation often involves the use of specific techniques devised for specific types of problems. There are specific methods for adding, subtracting, multiplying or dividing and more calculations such as squaring numbers or its opposite [square] "root finding". And even specific methods depending on the numbers used, such as "multiply by 10" or "multiply any 2-digit numbers", or "square numbers near 50".