MrShorty: I want to replace the formula in 'O14' & 'O15' where I would just call a UDF. something like @InterpVol("Table1",O14,O15,"ExtA") for 'O14' and the UDF would do the rest. Then a separate UDF for 'O15', something like @FindB("Table2",....) for it's variables.

I'm not sure how to manipulate the UDF in the workbook I attached to do what I what. Table1 & Table2 are actually in another workbook (it will be open).