Can someone help me clarify this equation.

=INDEX(SLOPE!D507:D606,MATCH(MIN(SLOPE!BI507:BI606 ),SLOPE!A507:A606))

I am asking excel to go to column D of the SLOPE workbook, match the
minimum of column BI.........All I get is the most current date.
Column D is a date, column BI is the minimum drop in equity. I wish to
retrieve the date of the minimum drop in equity from column BI.

Any help would be appreciated.