cExams.net
Do You Know
Questions & Answers on General Knowledge.

Question:
Why do scantron-type tests only read #2 pencils? Can other pencils work?
Answer:
The #2-pencil requirement is mostly historical. Because modern scantron systems can use all the sophistication of image sensors and computer image analysis, they can recognize marks made with a variety of materials and they can even pick out the strongest of several marks. If they choose to ignore marks made with materials other than pencil, it's because they're trying to be certain that they're recognizing only marks made intentionally by the user. Basically, these systems can "see" most of the details that you can see with your eyes and they judge the markings almost as well as a human would. The first scantron systems, however, were far less capable. They read the pencil marks by shining light through the paper and into Lucite light guides that conveyed the transmitted light to phototubes. Whenever something blocked the light, the scantron system recorded a mark. The marks therefore had to be opaque in the range of light wavelengths that the phototubes sensed, which is mostly blue. Pencil marks were the obvious choice because the graphite in pencil lead is highly opaque across the visible light spectrum. Graphite molecules are tiny carbon sheets that are electrically conducting along the sheets. When you write on paper with a pencil, you deposit these tiny conducting sheets in layers onto the paper and the paper develops a black sheen. It's shiny because the conducting graphite reflects some of the light waves from its surface and it's black because it absorbs whatever light waves do manage to enter it. A thick layer of graphite on paper is not only shiny black to reflected light, it's also opaque to transmitted light. That's just what the early scantron systems needed. Blue inks don't absorb blue light (that's why they appear blue!), so those early scantron systems couldn't sense the presence of marks made with blue ink. Even black inks weren't necessarily opaque enough in the visible for the scantron system to be confident that it "saw" a mark. In contrast, modern scantron systems used reflected light to "see" marks, a change that allows scantron forms to be double-sided. They generally do recognize marks made with black ink or black toner from copiers and laser printers. I've pre-printed scantron forms with a laser printer and it works beautifully. But modern scantron systems ignore marks made in the color of the scantron form itself so as not to confuse imperfections in the form with marks by the user. For example, a blue scantron form marked with blue ink probably won't be read properly by a scantron system. As for why only #2 pencils, that's a mechanical issue. Harder pencil leads generally don't produce opaque marks unless you press very hard. Since the early scantron machines needed opacity, they missed too many marks made with #3 or #4 pencils. And softer pencils tend to smudge. A scantron sheet filled out using a #1 pencil on a hot, humid day under stressful circumstances will be covered with spurious blotches and the early scantron machines confused those extra blotches with real marks. Modern scantron machines can easily recognize the faint marks made by #3 or #4 pencils and they can usually tell a deliberate mark from a #1 pencil smudge or even an imperfectly erased mark. They can also detect black ink and, when appropriate, blue ink. So the days of "be sure to use a #2 pencil" are pretty much over. The instruction lingers on nonetheless. One final note: I had long suspected that the first scanning systems were electrical rather than optical, but I couldn't locate references. To my delight, Martin Brown informed me that there were scanning systems that identified pencil marks by looking for their electrical conductivity. Electrical feelers at each end of the markable area made contact with that area and could detect pencil via its ability to conduct electric current. To ensure enough conductivity, those forms had to be filled out with special pencils having high conductivity leads. Mr. Brown has such an IBM Electrographic pencil in his collection. This electrographic and mark sense technology was apparently developed in the 1930s and was in wide use through the 1960s.
--- >>>
More Questions:
  • What is a shockwave and a sonic boom?
  • How did the Inuit hunt?
  • What do the distress letters SOS stand for?
  • Can one's health be adversely affected by the use of certain wraps, films, or containers, when heating food in the microwave?
  • Why is smoking cigarettes bad for your health?
  • What is the Arctic tundra?
  • Are some musical instruments really made of vegetables?
  • What effects, if any, does storage temperature have on the height of a tennis ball's bounce?
  • During the American War of Independence, which country contributed the most soldiers to fight alongside the British?
  • How does suntan lotion work to prevent ultraviolet rays from damaging your skin?
  • How was mail delivered before there were mail carriers?
  • How are incandescent light bulbs made?
  • Why do we carve jack-o-lanterns for Halloween?
  • My nose sometimes bleeds while I play sports or after practice. Why?
  • What is a barometer, how does it work, and why is it useful in predicting the weather?
  • What do the astronauts wear in space?
  • How do neon lights work?
  • Is it possible to count to infinity?
  • Why are some plays staged again and again?
  • What is analog? I hear about digital audio being better than analog, but nobody defines what analog is.
  • Why does water stay in the straw when a finger is pressed over one end? How does sealing off the one end make the pressure less?
  • When you traveling in a jet plane, why do objects on the ground look as though they are still or moving slowly?
  • How does a steam engine work?
  • Which snake builds a nest to care for its young?
  • What are the reflectors on my bike or scooter for?
  • Awesome Gifts For Christmas
  • Benefits of Peppermint
  • Class 8 - Force And Pressure
  • Top American Roadside Attractions
  • 101 Ideas to Make the World a Better Place
  • Benefits of Ginger

  • Chourishi Systems