The number 0 can help with this;
Number of leading zeros in the hash of every 100,000 blocks
Block 1 - 08
Block 100,000 - 11
Block 200,000 - 13
Block 300,000 - 16
Block 400,000 - 16
Block 500,000 - 17
Block 600,000 - 18
Block 700,000 - 19
Block 800,000 - 19