Base 10, or decimal, is a number system that uses the digits 0 to 9. The value of each digit is determined by its place value, with each place to the left being ten times greater than the place to its right. For example, in the number 642, the 6 represents 600 (6 x 100), the 4 represents 40 (4 x 10), and the 2 represents 2 (2 x 1), which sums to 642 when written in standard decimal form. Decimal also uses positional notation to explicitly show the exponent of ten for each place value.