One maths class we were only warned that we had to use Euclidean paper.
I did great in exams with cheat sheets, but poorly in the few truly "open book" exams, because I didn't know how to properly prepare for an open book exam. My silly undergrad brain thought "Woohoo, open book, I guess I don't have to study all this stuff, I can just look it up when I get there" which led to two hours of feverishly flipping back and forth in the book.
I did great in exams with cheat sheets, but poorly in the few truly "open book" exams, because I didn't know how to properly prepare for an open book exam. My silly undergrad brain thought "Woohoo, open book, I guess I don't have to study all this stuff, I can just look it up when I get there" which led to two hours of feverishly flipping back and forth in the book.