>What's the "PK"?????

PK = Primary Key; whatever you use to uniquely identify a given record. It's not recommended that you use the RECNO(), especially with buffering, since newly appended but uncommitted records can have a negative record number; some field or set of fields is better technique. Many people (including me) put a surrogate key that acts only to identify a specific record without carrying any other data about the record to act as a unique identifier for setting up relations between tables.