Andrew
There are many new statistical/Pareto type features coming. As we discussed, for the analysis you are doing, the best approach is to use formulae to calculate the percentage of total cases represented by each category, then plot these percentages on a Bar View where the width/spacing/number of bars has been restricted to just enough to show 80% of the cases, etc.

Andrew - just stumbled upon your post and I had the same issue. I create a formula called Pareto which is:

SUBSET_SUM([GBP Spend],SUBSET([Supplier]))/SUBSET_SUM([GBP Spend],SUBSET())

I then have a column which shows for each line the percentage of spend for each supplier as a proportion of the whole data set. I have another field that is SUBSET_SUM([GBP Spend],SUBSET([Supplier])) which I use as a device to change the range. I have a table which shows the Pareto column and also sums it at at the bottom. Changing the range then changes the percentage at the bottom of the table. If you want to sub divide it further, use SUBSET2 or SUBSET3 functions as the second parameter of the SUBSET_SUM function. (I hope all that makes sense).

In your example:

SUBSET_SUM([Volume],SUBSET([Caegory])

and

SUBSET_SUM([Volume],SUBSET([Caegory]))/SUBSET_SUM([Volume],SUBSET())

Please add your votes, specifications and use cases for Pareto here:

http://forums.visokio.com/discussion/665/idea-pareto-custom-rangess

Are there any features in 2.8 beta that will enable pareto charts to be produced please?