The manual calculations and formulae. They were a bit complex. The formulae were a bit abstract. Not easy to understand. Not intuitive. I sat beside an SSIS guru and he took one look at them and said “Good luck Geoff”. I coded them all and after I left, I got a call from a techy there asking me what they were all about! He hadn’t a clue how to unravel them, even with documentation. Also, they managed to accidentally delete them all. No idea how they did that. After a few panic-filled phone calls, they dropped the whole thing. It was a mess there. Glad I left.