lol the #2 pencil thing teachers say isn't completely serious. it's somewhat of a blanketing general rule to prevent freak accidents, like the rule about electronics on an airplane. Do you really think playing pokeman green on your gameboy pocket on a flight will completely fubar the airplane's navigation and communication systems?
back in the day, they actually sold pencils that weren't #2. looking through my parents' 80s vintage pencil bag, there's no way some of those pencils will register on a scantron. that rule is from way back then, and kinda still sticks. these days, it's very hard to buy any pencil that isn't #2 and almost all mechanical pencil lead sold to general consumers is #2, hb, or around there. let graphical mechanica iron out the wrinkles in your daily life