Pivot tables with calculated fields (one column divided by another)

Hi,
I'm using a pivot table to display my data in a more coherent way, but have run into some problems with create a calculated field. The row labels are dates (grouped by months and years), and there are two columns which are the count of A and count of B. Please note that they are counts, ie. not the sum. I'm trying to add a third column which would show count of B as a percentage of count A. However, pivot tables don't seem to handle this very well, as instead of using the count of each variable, it sums them. Any ideas on solutions?

Thanks in advance!

Originally Posted by GeneralDisarray

can you post an example to play with?

Sorry for the late reply! I've attached a simply workbook that you can play around with to see what I mean. The first pivot table shows that what I would like to do is possible for days, but when I group it by months and years (in second pivot table) it just shows #DIV/0!. Is there any way to get around this?

Thanks!