Crystal Reports Graph

I'm working on a project in VB 5.0 with Crystal Reports 4.5 . (Primitive , u may think, but that's the version I have!). In one of the reports I'm supposed to make a graph on a 'formula field' but I observed that only certain types of formulae were being allowed for being plotted . The formula , I created performed calculations on multiple records of the same field. When I go to Graph Wizard, it does'nt allow me to plot a graph on the formula field as the Y-coordinate.
I would be grateful to anybody who helps me out!