base 12 is a positional numeral system with twelve as its base. It uses 12 different digits for representing numbers. The digits for base 12 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, and b.

base 28 is a positional numeral system with twenty-eight as its base. It uses 28 different digits for representing numbers. The digits for base 28 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, and r.