I Found the solution.
I made a subreport for difference column only, with same parameters as in main report and
called the subreport after linking i.e. crystal report asks for linking the report parameters
on subreport addition.
Question
I have made crosstab report with Section (Fuel/Lube) and Nature (Finished/Semi-Finished) as row headers and month (September/October) as column header and value as summary field.
What I want is another column having difference for each row summary field for the given months i.e. September, October,....
Solution
I Found the solution.
I made a subreport for difference column only, with same parameters as in main report and
called the subreport after linking i.e. crystal report asks for linking the report parameters
on subreport addition.