How to convert calculated fields into measures OTBI

Summary:

We're using data from the Recruiting - Recruiting Real Time subject area. We need to create a performance tile to display Total Openings Left to Fill however the values returned by "Facts - Requisition Counts"."Number of Openings Left to Fill" is too large compared to when we compute this using the difference between "Job Requisition - Basic Information"."Number of Openings" and "Job Requisition - Basic Information"."Hired Count". We realize that performance tiles can only be created from measures but the manual calculation does not seem to want to be changed into a measure.

Content (required):

Subject Area: Recruiting - Recruiting Real Time