Display graph information by trimester

[Fysh]

I am working on a project for statistical information. Some of the items
need to be placed into a graph. However, their requirement is to have it
displayed by trimester. On my reports form I allow them to select the
criteria they are looking for with a start and finish date. Is there a way
to display the information on the graph by trimester, if so how?

for instance
4 6 7 3
total
1-04 2-04 3-04 1-05
trimester

Thanks