ACS,
You're technicaly correct of course. Perhaps I was trying to get my point across a little..........simplisticaly
If I remember correctly, the good book says that Tristar performance corrections for contaminated ops are a best guess, not the result of trials, and do not give normal perf A saftey margins. There probably are circumstances when you would do it, but they are few and far between. Although these days........
Take care out there,
Arty F