A base is a counting system. Base 10, or "decimal" uses the digits 0,1,2,3,4,5,6,7,8, and 9. we have digits 0,1,2,3,4,5,6,7,8,9,a,b,c,d,e, and f. Notice that 10 is a, 11 is b... and we go up to 15 (f), which is 16-1, instead of the 1s, 10s, and 100s places like decimal,