[Koha] When importing records, question about matching rule

When importing records, my matching rule works when ISBN matches identically in both records .. so ... I need to modify my ISBN matching rule so that it matches books that MAY have the prefix 978 in front of the ISBN. Does anyone know how to modify the matching rule so that 978MATCH and MATCH will match? My current rule is Tag 020 (ISBN) Subfield a Offset 3 ( I tried 3 so it would ignore the 978 but this did not work) Length 0 Normalization rule : blank Happy Holidays everyone!!! David W. Hartman Global Business Technology Strategy Library Team Disney 336N