Hexadecimal
In the decimal system, the first digit is the one's place, the next digit to the left is the ten's place, the next is the hundred's place, etc.  In hexadecimal, each digit can be 16 values, not 10.  This means the digits have the one's place, the sixteen's place, and the next one is the 256's place. So 1h = 1 decimal, 10h = 16 decimal, and 100h = 256 in decimal.