My senior year of high school my thermodynamics class had a test a week and threw out the lowest 2 test score. Each test was open book, any book, but there wasn’t enough time to learn during the test. You would get a B if you laid out the equations, put in the correct numbers but did not do any arithmetic.
I also liked classes where you could use a 3x5 card for whatever information you wanted to put on it. You learn a lot when hand lettering at a 2 PT size.
I never was good at arithmetic so I made a pact with each class (speaking high school now) that if the problem was correct, it was correct and did not need to be reduced to lowest terms (Etc.) So if the answer was one half and a student wrote 211/422, that was correct. I would also accept 0.5
I tried to use this to teach that numbers in different forms were alike in value. Of course they had to get the sign right if the answer was negative.
This also meant that I had to be alert for these issues when grading. Also, if a formula was correct but not simplified, (unless the problem was to simplify) I would take the answer as correct. So if the answer was tan x, I would accept (Sin x/ Cos x)
The idea of a cheat sheet is good too, but I usually allowed all pages as long as homework was on some of the pages. In my classes you could not get above a C grade if your homework score was zero. And sometimes homework counted so much that the best you could do with no homework would be a D.