I was just talking to a student about this and he mentioned a new method of
cheating that I hadn't considered. On the inside of the black calculator
cover write equations (or anything else) lightly in pencil. Unless the
lighting is just right, you won't see anything. Someone glancing ove from
the end of a row certainly wouldn't see anything.
A guess that a determined cheat can usually find a way. Hopefully most of
the students are mostly honest. And as others have mentioed, just having
the equations is no substitute for understanding the material.