To locate matches across pairs of lists without unique identifiers it is sometimes necessary to compare strings of letters. String comparators are used in production computer matching software during the Post Enumeration Survey for the 1990 U.S. census. A string comparator metric is described that partially accounts for: (1) typographical variation in strings such as first name or surname; (2) decision rules that use the string comparator; and (3) improvements in empirical matching results. The string comparator metric for comparing partially agreeing strings extends the Jaro string comparator. How general methods of accounting for partial agreement fit with the Fellegi-Sunter (I. P. Fellegi and A. B. Sunter, 1969) model of record linkage is described. A formal method of modeling how to adjust matching weights between pure agreement and pure disagreement is presented. The procedure is illustrated for files for which the truth of matches is known. It is demonstrated that the theoretical rules of Fellegi and Sunter are still valid when general weighting adjustments accounting for partial agreement are performed. Eight tables contain illustrative data. (SLD)