To make a Calculated Column that references another Calculated Column, you have to leave the design process and to go the report itself. On the right list, click on the calculator icon, labeled "Calculation". The click "Calculated Column". Click Add to create a new one. Go to the "Manage Scripts" tab, and under the keywords and functions, you will see "fields". Choose the field that is you calculated column, and you can work it into your script as normal. 

Thank you, Morgan.  That worked perfectly!

Can filter fields be used in the calculated collumn?