Instead of using month as the column field, you should create conditional formulas for summary fields, one for each month, like this:
//{@prevmo}:
if {table.date} in dateserial(year({?Date}),month({?Date})-1,1) to
dateserial(year({?Date}),month({?Date},1)-1 then
{table.callID} else
tonumber({@null})
//{@currmo}:
if {table.date} in dateserial(year({?Date}),month({?Date}),1) to
dateserial(year({?Date}),month({?Date})+1,1)-1 then
{table.callID} else
tonumber({@null})
...where {@null} is a new formula you open and save without entering anything. Then to get the difference right click on the {@prevmo} summary->format field->suppress->x+2 and enter:
whileprintingrecords;
numbervar prev := currentfieldvalue;
false
Then select the {@currmo} summary->format field->suppress->x+2 and enter:
whileprintingrecords;
numbervar curr := currentfieldvalue;
false
Then create a formula {@0} like this:
whilereadingrecords;
0
Add this as your third summary and then right click on it->format field->DISPLAY STRING->x+2 and enter:
whileprintingrecords;
numbervar prev;
numbervar curr;
totext(curr-prev),0,"")
Go to the customize style tab and select "horizontal" and "show labels" for the summary fields. Then edit the labels as necessary.
-LB