Calculate change between details in report (query?)

[tk]

Dear All,

I am creating a report whereby I list a variety of conditions (C1-3)
and sum up the number of projects where this condition applies to.This
whole thing is grouped by year:

C1 C2 C3 Total C2/3 Change C2/3 Change C1
Y1 3 2 6
8 / /
Y2 2 5 8 13 + 62%
-33%

How can I calculate the change from year to year as indicated in the
table above? I am sure there is an easy way ...

By the way, the report is based in a crosstab table, which may be the
first problem.

TIA, Tom