Base-16 number system. Since there are 16 hexadecimal digits (0 through 15) and only ten numerical digits (0 through 9), six additional digits are needed to represent 10 through 15. The first six letters of the alphabet are used for this purpose. Hence, the hexadecimal digits read: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F. The decimal number 16 becomes the hexadecimal number 10. The decimal number 26 becomes the hexadecimal number 1A.