I recently upgraded (not by choice) so I will review all the posts and take a look if I find your db here.
EDIT
OK, I've looked at the report and
a) have no idea where you'd put the result of the calculation or whatever else you might do with it
b) the report is based on a table, which makes for very limited capability with respect to how you can present data
c) where or how you intend to provide the month...
On one of your forms (if so, which form and which control)?
A query parameter prompt (not a great idea)?
??
There's a whole bunch of other strange looking things going on, but that's OK - we are all noobs in the beginning
I could start by basing the report on a query based on the table, but I'm not sure how much 'altering' you're prepared to accept. Hate to do a bunch of work if you're just going to discard it.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.