Report builder - limit to 3 fields in Y-Axis?

Report builder - limit to 3 fields in Y-Axis?

I can only drag three fields into the Y-Axis on a bar graph.  Is this a limitation?  I have four things to graph, pounds, dollar value of pounds; time, dollar value of time.  Pounds and dollar value of pounds share the same scale, so time and value of time should work too.  Right now I have to choose either time or value of time to display with the pounds/dollar value.  I'd like to show all four.