The general principal seems to be replacing being distance X from the truth with probability 1, with being distance X/10 from the truth with probability 0.99 an

The general principal seems to be replacing being distance X from the truth with probability 1, with being distance X/10 from the truth with probability 0.99 and distance X*10 from the truth with probability 0.01. This is consistent with another reply which states that it guesses the true letter (sometimes incorrectly)