MDX query for aggregate a measure that is a difference of a max\min measure

Hi,

I have a fact table that is linked to a dimension table( customer ), and in this table I have a column( measureA )
In my SSAS I have two measures: MaxMeasureA( max value os measureA ), and MinMeasureA( Min value of measureA )

What I need: Separating by day, I need the aggregation of the difference Max-Min of all my customers

I know how to do that for each single customer, create a member with Max-Min and separate by customer in the axis. But if I remove the separation by customer in the axis, my query get the MaxMeasureA of all customers, and substract for the MinMeasureA of all customers, and this a wrong value, example: The min/max de customer1 is 10/20, and the min/max de customer2 is 999990/1000000, and the total daily difference will be 999990( the real value should be 20 ).

So I need to calculate the max\min for each customer separately, and after that, aggregate all these values. How can I do that?

Best Regards,

Luis