= Casting out nines
{wiki=Casting_out_nines}
Casting out nines is a mathematical technique used primarily for error detection in arithmetic calculations, especially addition and multiplication. The method relies on the concept of modular arithmetic, specifically modulo 9. The basic idea is to reduce numbers into a single-digit form called a "digit sum" or "reduced digit" by repeatedly adding the digits of a number until a single digit is obtained. This final digit, known as the "digital root," can be used to verify calculations.
Back to article page