EAGAN, Minn. - In schools, April is peak season for standardized testing. For many students, that means its the season of No. 2 pencils and scantron forms.
In fact, if you were in school after 1972, you've likely filled in a few bubbles yourself. And guess what! The machine relies on science to give each student an accurate score.
Of course one of the rules when you're taking a test on a scantron: bring a Number 2 pencil. It's all because of what we call the pencil lead. It's made up of clay and graphite, which contains carbon. The clay just holds it together but the scantron sees this carbon and that's how it knows what mark you made.
The ink in pens contain little to no carbon, so they don't work.
Scantron testing is used worldwide but the technology and machines are developed right here in Eagan at the company's world headquarters.
Todd Radtke of Scantron breaks it down. "We're actually using physics and a light source... Infrared light. And infrared reflects everything except carbon. And so the carbon that's in that pencil lead shows up in that scanner, we see it. We see only what the student wrote on the piece of paper."
Another reason for the number 2: you can erase it if you change your mind.
"Erasure can remove some of the carbon, you'll always have traces left behind. So this could be an example of an erasure and this is an intended mark left by a student. We actually have intelligence that can actually vary between these two to know which one is the actual mark," says Radtke.
So no need to stress if you want to change an answer.
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