Given a fact table of performance values of "Avg Disk sec/read", recorded at 1 per hour.

I only care to see the averages "per day".  So, currently, i only have a time dimension to the day level.  By default the cube sums the 24 values it finds each day and presents that sum to me...not what i want.  I changed the aggregation to "Average of children"... but that didn't change...it appears to affect the way two days are aggregated.

What's the mechanism to achieve this averaging of the core cube values?