Show Percentages of crosstab column Total?

Summary

Need help creating a view that show trending over time (daily, weekly etc) in the % split of our Product IDs..

Content

I know this is possible but seem to be unable to build myself, and but have spent forever searching this forum without luck:   

Goal:  We want to create a simple chart that presents the ongoing daily trend of the % split of our incidents by product.   

It's easy to produce this with the absolute numbers:  Columns are: DateGroup "Interval", Product ID, and Count of Incidents Created.   Then I set up a cross tab with "Product ID" as the Row Field,  "Interval" as Column field, and "Incidents Created" as the output field.    This provides a chart showing the daily trend of our incident volumes by each Product.