Each block has a score based on the verifier that signed it. A lower score is better than a higher score. At each height, an incremental score is calculated relative to the block at the previous height, and the total score of a block is the sum of all incremental scores back to the frozen edge.
For a block signed by an existing verifier, the incremental score is zero plus four times the difference between the previous block's cycle length and this block's cycle length. If the verifier is not active in the mesh, five is added to the incremental score.
For a block signed by a new verifier, the incremental score is negative six plus four times the verifier's position (zero-indexed) in the new-verifier vote total list. Twelve is added to the score of a new verifier not present in this list, which is limited to a maximum size of three.