I hope the topic fits in the table calculations category.

To make the example simple imagine I have a table of number of sessions by URL and then I add a pivot for a boolean flag.

How do I create a measure that only shows once as a difference of the first from the second (or the other way)?

Pivot_offset would give me a custom measure, of course, but it will show twice in the result table with the first (or second) column empty.

Any ideas?