how to count the number of row and use the number in another formula

I want count the number of rows, also I want use that number in my formula. I can use insert summary to get the number, but I do not know how I can use that number in my another formula. I do not need the number of rows on my report, but I need that number to calculate the formula.

Is there another way I can count the rows? Thanks!

[450 byte] By [cjcclee] at [2008-1-7]