Help, I'm going nuts.

I have a challenge that is so far beating me.  I have a pivot table that
summarises sales values and margins by month and I had no problem in adding a
calculated field with a monthly budget figure and charted this quite easily.

So far so good.  However, I now need to break these numbers down by product
groups, but I can't get the calculated budget field to break down by product
group - I have tried using an IF statement in the calculated field but it
just returns the ‘false’ value (i.e. if, true, false).  Also the total isn’t
adding up, e.g. the budget part of the table resembles:

Month    group a    group b    total
Jan    100    100    100
Feb           etc.

The chart has gone from clear and simple to a techicolour nightmare – but
I’ll worry about that when I have got the pivot table sorted.

Any help is much appreciated.

Regards,

Nigel