Mick,

Try another calculated field that uses your existing one, something like:

IF

    {INCLUDE [Sub-Category] : SUM(Sales)} == {EXCLUDE [Sub-Category] : MAX([Sales of Sub Category])}

THEN [Sub-Category]

END

That will allow you to compare the sum of Sales at a Sub-Category level with the Sales for the Max Sub Category and give you the sub-category where the two values are equal.

Hope that helps!

Joshua

Hmmm...  works for me, but there may be something I'm not seeing that changes things in your case.  Do you happen to have a sample workbook or even a screenshot of your setup?

-Joshua

Two comments:

1) If you want to read a long post on the subject check out LOD Expression Remix – Finding a Dimension at a Lower Level | Drawing with Numbers.

2) Since LOD expressions are doing separate aggregations than the vizLOD when floating point numbers are involved you can end up with different results, you should either round them or convert to integers prior to doing the comparison. There's a comment on this just before the Conclusion of Bora Beran's fantastic post introducing LODs: What’s new in Tableau 9.0? Part 2 – Level of Detail Expressions « Bora Beran .

Jonathan

Awesome!