Eliminate Top & Bottom 20% of records from detail section

Crystal Report

I have two groups, Group1 is by PartNum and Group2 is by WorkCenter. I
also have 1 detail section. I want to only show/select the middle 60% of
records, or to reword that I want to eliminate the top 20% and bottom
20% of the detail records. How do I do this? I have tried using the Nth
Largest and Nth Smallest and even Pth Percentile functions but I just
don't seem to know how to use them correctly since I need this done at
the detail level and not group level.

Thanks



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