Sorry for the late response! It would be a percentage of the number of characters changed (either inserted or deleted) to the original character count. I think it cannot be both because the percentage needs to be a 100 and no more (so if a sentence had 100 characters, and lets' say the edit included deleting the entire sentence (100 deletions) and then adding (about 50) characters, the ratio should not exceed 100%. So, in the end, I'm not sure but if I visually saw a sentence full of deletions/insertions I would say it was 100% revisions, but I am not able to put a formula to it. Any suggestions?