When I was in school, a lot of testing, including college placement exams, was scored by means of electromechanical devices ("Scantron") which identified answers by testing for the difference in conductivity produced by filling in one of several multiple-choice bubbles with pencil lead. Using a pen would result in a score of zero because the machine couldn't tell you had filled in anything. I don't know if this was used at university level because I never ended up going, but it certainly was used on the placement exam. (Four hours of multiple choice questions with exactly one -- one! -- essay section to break up the monotony, my God, I was ready to die afterward.)