Sample workbook available?
Joe that did the trick! Thank you very much.
I did some reading in the manual and found some extra info under the topic Aggregate Calculations:
"About Aggregate Calculations
Suppose you want to analyze the overall gross margin for every product in your data source.
One way to do this is to create a new calculated field called Margin that is equal to the profit
divided by the sales. Then you could place this measure on a shelf and use the predefined
summation aggregation. In this scenario, Margin is defined as follows:
Margin = SUM([Profit]/ [Sales])
This formula calculates the ratio of profit and sales for every row in the data source, and
then sums the numbers. That is, the division is performed before the aggregation. However,
this is almost certainly not what you would have intended because summing ratios is
generally not useful.
Instead, you probably want to know the sum of all profits divided by the sum of all sales.
That formula is shown below.
Margin = SUM( [Profit]) / SUM([Sales])
In this case, the division is performed after each measure is aggregated. An aggregate
calculation allows you to create formulas like this."