The match rating approach (MRA) is a phonetic algorithm developed by Western Airlines in 1977 for the indexation and comparison of homophonous names. The algorithm itself has a simple set of encoding rules but a more lengthy set of comparison rules.The main mechanism is the similarity comparison, which calculates the number of unmatched characters by comparing the strings from left to right and then from right to left, and removing identical characters. This value is subtracted from 6 and then compared to a minimum threshold. The minimum threshold is defined in table A and is dependent upon the length of the strings.