Calculated number fields in Reporting?

[Ricky Lin]

I managed to figure out how to get the Resolution Time (ResolutionDate - Created) thanks to the wonderful community!  However, I'm having challenges putting this in JIRA Reports such as Pie Charts, Two-Dimension Filter... etc

The Project Manager would like to be able to see this on a weekly bases in a visual way but the Calculated Number Field does not seem to be a selectable option...

Anyone?