Duplicates in custom reports

Duplicates in custom reports

I made a custom open potentials report by territory.  The report contains many duplicate line items for potentials. 

It seems that if the sales person changed the probability value assigned to a given potential, then a duplicate line in the report is created.  On the report, all potentials of the same ID are listed at the latest probability rating. 

How can I eliminate these extra lines and view only one line per potential?