You can have JMP script this for you if you are willing to create 2 extra columns--
1) select the columns T7 through T7H, then right-click on one of the column headers in this group and select New Formula Column > Combine > Maximum.
2) Repeat the process above, but using the columns T8 through T8H.
3) Select these 2 newly-created columns, then right-click on one of their headers and select New Formula Column > Combine > Difference (reverse order).
If this doesn't work for you because you don't like having the 2 extra columns, take a look at the formulas in the columns you created in step 1 and 2 above. These will show you how to write the formulas you need... basically you will just subtract the first of these formulas from the second to create your single "master" formula.
Cheers,
Brady