Mystery #171 - Testing Etiquette

Joey Presents: Great Mysteries of the Universe Mystery #171 - Testing Etiquette I could go on for hours about bubble sheets, no-talking rules, and test booklets. However, my investigation into the mysterious has led me instead to the conundrum of the #2 pencil. So I get the pen vs. pencil argument. I mean, I make lots of mistakes, so the whole eraser thing comes in really handy. No, my question is instead about the number. Why number 2? I know it signifies something about graphite consistency and darkness, but why a two? Depending on who came first, the scantron guys or the pencil guys, SOMEONE obviously made a bad call. #2's obviously have a corner on the market, why not make THEM Mystery #1's? Or, on the other hand, why not calibrate the machines to read Mystery #1 pencil marks? The two thing just seems silly. We won't even go into the whole "#2 vs HB" discussion, my blood pressure just can't take it.