Hello, I have a cross tab with summarized results as follows (example below)

                         Jan-Jun                                           Jul-Aug
                  out of network                                   out of network
                    vol        %                                               vol    %
Cardiac         400      66%                                          262    52%

In my cross-tab I want to be able to add a formula to take the 52% minus the 66% and show -14% for cardiac etc..., Easy in excel but I am stumped in crystal

thanks