Pivot Table Calculated Field Challenge

Hi. I'm seeking a solution to a Calculated Field challenge I'm faced with. I have a database of 700 assignment records. Within each record is a field named Job Title and a field named ST Rate. I am trying to calculate the difference between the high ST Rate and low ST Rate for each Job Title.

In my Pivot Table I have the Job Title as a column field. I pulled ST Rate into the data area and set it to MAX ST Rate. I pulled it in again and set it to MIN ST Rate. I attempted to create a Calculated Field to subtract the MIN ST Rate from the MAX ST Rate, but MIN ST Rate and MAX ST Rate are not available fields in the Calculated Field wizard.

ANy suggestions or ideas? Thank you.