I had an Econ teacher that did something similar but it was a note card. Thing was she reused the same bank of questions every semester and provided a study packet of sample questions that was a super set of the questions on the final. Some kids got wind of this and encoded the answers to the study packet on the index card. They were bizarrely accused of cheating.
I know someone who did something similar in analog electronics. The teacher asked them to come to their office, and asked them a few questions. As the student couldn't answer them, the perfect score was commuted into a failing grade.
Regardless of how you approach this, an exam is here to evaluate your level of proficiency on the topic at hand. If you sidestep this, that would be called cheating.
