[Koha] Help with MARC record matching rules

[Joel Ewy]

Anybody know how to properly specify matching rules for importing marc
records?  I take it that if the rule works, it should show a match in the
appropriate column on the "Manage staged MARC records" page before
importing.  I don't trust my zebra indices, and it appears that the match
checks are supposed to match directly between the imports and the database.
 That's what I want.  All I get is "no_match", so I assume I've specified
the matching rules incorrectly.  What am I doing wrong here?

Matching rule code: MatchISBN 
Description: Match the ISBN Required 
Match threshold: 100 Required 

Match points
Match point 1 | Add match point | Remove this match point
Search index: ISBN
Score: 101 

Matchpoint components
Tag: 020
Subfields: a
Offset: 0
Length: 0
Normalization rule: 

Required match checks
Match check 1Add match check | Remove this match check
Source (incoming) record check field
Tag: 020
Subfields: a
Offset: 0
Length: 0
Normalization rule:  
Target (database) record check field
Tag: 020
Subfields: a
Offset: 0
Length: 0
Normalization rule: