I generally do not allow crib sheets on mid-term exams and do allow
them on finals. I also talk about methods of "rationalizing" a formula
so that they "do not have to memorize it," and the rationalizations are
of course to understand the physical meaning of the formulae and use units.
I then ask on the mid-term for the method they are using to remember one or more
formulae. Since I am asking about understanding the formulae on the exam,
they see the need to work on it. I now very seldom see wrong formulae used
on problems. Perhaps this procedure works better with the honors students
I am teaching than it would in a nonhonors class.
On the final, the crib sheet is restricted to *one 3x5 card*, under
threat of confiscation. Since the space is strictly limited, they have
to think about what is important enough to put on the card. Both by my
observation and the comments of past students, once the card is prepared
they seldom have to look at it.
It seems to me that the goal is to get them to think; any tool that
leads in that direction is acceptable.