[LordSkie]

as eagle said, level plays a big part too.

But maybe accuracy or dexterity plays it's part too...

I'm doing complex meth lab nearly 100% with lv 6 endurance, and was doing simple comfortably with 3, but I don't remember ever having below 3 intel, I was on that for months, only recently moved up to 6 with PE400 and java programming.

I think it's mainly level that has the effect. At a lower level, you'll need around 8-9 intel to do complex, 4-5 for simple. Maybe higher still if you're really low level.