Levenshtein distance
The three atomic 'changes' considered in this measure are: inserting a single symbol (usually a character, like letter, digit etc.), deleting a single character, and replacing (substitution) a single character with another one. Moving a character to another position in the text, swapping two characters, as well as adding, deleting or replacing longer blocks of characters (like words in a sentence) are not counted as single changes in this measure.