Function probability_from_one_char_sub 

pub fn probability_from_one_char_sub(
    source: char,
    destination: char,
) -> FloatType

How likely one length was misread as another: music21’s getProbabilityFromOneCharSub. A length doubled or halved any number of times is 0.0165 for each; a rest read for a note of the same length an addition, the other way an omission; a note read as a rest 0.003; and anything else an omission and an addition at once.