…well, maybe the true reason isn’t that the machine won’t recognize the pencil lead, but that it could cause a catastrophic explosion as seen in XKCD’s comic.

Everytime I took a ScanTron test, the teachers harped incessantly about using a #2 pencil. I mean, what would happen if you didn’t? You would fail if you didn’t have one because the reader couldn’t see the graphite? The paper would disintegrate due to the sheer amounts of pressure applied under a harder lead? The tectonic plates would shift causing the big earthquake that’s due any day in Charleston? The world economy would collapse? Oh wait, that last one is in the process…Anyway, quite a funny take on the subject in the comic.

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