Today I found out why you used to have to use #2 pencils when using scantron forms.

Now, you might be saying, “Used to? Don’t you still have to?”  It turns out, despite what pretty much all teachers will tell you, not really.  Modern scantron systems are quite high-tech, using image sensors and sophisticated image processing algorithms.  These algorithms can even pick out which oval has the strongest mark.  So if your test is being processed by one of these newer scantron systems, you could fill out every bubble on the scantron and it would simply pick the darkest shaded bubble in each row and assign that as your answer.

As such, you can use pens, pencils, and even printer toner or ink, if you want to run your scantron through a printer to mark all your answers.  Pencils are obviously still preferred over pens, giving you the ability to erase your answer.  Also, generally speaking, you still want to use some form of grey to black colored marking device to ensure your scantron form is read perfectly. Although, anecdotal evidence has shown that even using shades of different colored ink or colored pencils will also work.  Though, at that point, the system isn’t necessarily going to read your form perfectly.  Further, if you pick a shade that is the exact color of the lines on the form, it might just ignore your markings.

On the flip-side, the early models of scantron machines were significantly less sophisticated.  They read pencil marks by shining light through the paper and Lucite light guides, which was then read through phototubes.  With this antiquated system, for an answer to be read, the light must be completely blocked out by the pencil marking to register correctly.

Graphite works well for this purpose because graphite molecules, which form tiny sheets of carbon, reflect much of the light that hits them and absorb most all the rest. It turns out, black ink isn’t opaque enough for these old scantron systems.  Further, lighter shades of graphite, such as in #3 and #4 pencils, weren’t sufficiently opaque enough for these old systems to perform without error, as is generally required.  #1 pencils would have worked fine, as they are darker than #2 pencils.  But, unfortunately, they also smudge easier when erased or accidentally rubbed with your hand as you mark the scantron form, increasing the possibility of a “false positive” when the scantron was reading your form.  So #2 pencils were just the right mix of darkness and hardness of the graphite/clay core to block the light effectively, while also not smudging too much.

One of the ways you can tell instantly whether whoever is processing your scantron is using a modern system or not is if the scantron is double-sided.  If so, it cannot be using an antiquated model, as the marks on the other side would interfere with the older system’s ability to correctly read the scantron form.  Modern systems have no such problem.

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Bonus Facts:

• Classically, scantron forms used blue ink for the lines and outlines to the circles because these old systems couldn’t pick up the light in the blue spectrum.  Newer systems are simply designed to ignore whatever color the scantron form was printed in.
• The core of most pencils, also called “lead”, is generally made of a mix of graphite and clay, with the clay functioning as a binding agent.
• Charcoal is also used for pencil cores, but primarily only for pencils specifically designed for drawing.
• Colored pencils usually have a type of waxy substance as their core, which is why colored pencil markings tend to smear when you try to erase them.
• The earliest scantron-like  machines used electrical conductivity, rather than light, to read forms.  Graphite is quite conductive, so the machines simply had a mechanism at each markable area location to make contact with the form and detect if an electrical current is detected across the area.  These systems were used as early as the 1930s.
• “Pencil” comes from the Latin “pencillus”, meaning “little tail”.
• While either mechanical pencils or regular pencils, with appropriately dark cores, will work on scantron forms, there is some evidence that mechanical pencils have an inherent disadvantage on timed tests that use scantron forms.  This is because “regular” pencils have wider tips than mechanical pencils.  Thus, the time it takes to fill in each bubble is significantly longer with a mechanical pencil over a “regular” pencil.  This won’t add up to much time on short tests.  But with timed tests with hundreds of questions, it can make an appreciable difference in the time it takes you to take that test.  On that note, perhaps some form of scantron form circle stamp, with erasable ink, should be developed, to further speed up the process of marking the form.
• Relatively pure graphite was extremely rare and valuable throughout most of history after its discovery in the 16th century.  Around that time, a huge pure graphite deposit was discovered near Cumbria, England.  To date, this is the only large pure deposit of graphite, in solid form, found on Earth.  Locals began using this graphite to mark sheep and other things.  The value of this substance quickly skyrocketed and guards had to be set at the entrance to the graphite mines.  They also would periodically flood the mines, when a sufficient stock of graphite was on hand, making it impossible for anyone else to steal any of it.
• Graphite deposits have been found elsewhere, but nothing nearly the purity and quality of this English find. Due to the impurities in these other deposits, the graphite from these deposits must be crushed into a powder to remove the impurities.  Eventually, a method was found to use this powder in pencil form, by using clay as a binding agent.  But before then, England had a monopoly on the world’s pencil supplies because only their graphite deposit could be cut and made into high quality pencil form, without any other processing needed.
• The earliest pencils were simply this graphite from England cut into sticks and then wrapped tightly in sheepskin, which was then sewn up.
• At this time, this graphite was thought to be some form of lead, or as they called it, “plumbago”, which was Latin for “lead”; hence why we still refer to it as “lead”, even though graphite doesn’t contain any lead.  The Germans also use this misnomer in that the German word for “pencil” is “Bleistift”, which means “lead stick”.
• The method for being able to use graphite powder for use in pencils was independently discovered by both Frenchman Nicholas Jacques Conté, in 1795, and Austrian Joseph Hardtmuth, around 1790.   During the Napoleonic Wars, France wasn’t able to import pencils from Great Britain, which had the only supply of pure solid graphite in the world.  Nicholas Jacques Conté, who was an officer in the army, discovered that if you mix the graphite powder with clay, you can then form this mixture into sticks and fire this substance in a kiln.  You also can vary the clay/graphite ratio to achieve different levels of hardness and darkness.  This is more or less exactly how pencil cores are made to this day.
• Conté was also the one that came up with the system to use numbers to signify the grade of the pencil, in terms of the hardness/darkness of the core.  This system was later adopted in the United States and is known as the Conté/Thoreau system (John Thoreau being the one who helped introduce it to the U.S.).  This system, translated to the pictured European system, is as follows: #1 = B; #2 = HB; #2.5 = F; #3 = H; #4 = 2H.
• In the European system, B stands for “Black” and “H” stands for “Hard”.  The more B’s, the softer the lead and darker.  The more H’s, the harder and lighter the lead.
• The tradition to paint pencils yellow was started in 1890 by the L. & C. Hardtmuth Company of Austria-Hungary.  In 1890, they introduced the Koh-I-Noor brand of pencil, which was a top-tier pencil.  The name itself was after the famed diamond.  This pencil was extremely popular, due to its high quality. Thus, many other manufacturers copied the color to make their pencils look like  Koh-I-Noor brand pencils.
• Today, yellow is the most popular outer pencil color in the United States and various other countries.  However, in Germany and Brazil, green is the most popular color.  In Australia and India, red with black bands at one end is the most popular outer color scheme for pencils.
• At the end of the 19th century, over 240,000 pencils were used up every single day in America alone.  Today, around 39 million pencils are used up per day, world-wide.
• Red Cedar was historically the wood of choice for making pencils with.  It had a favorable smell and didn’t splinter easily.  However, by the 20th century, Red Cedar was in very short supply the world over and pencil makers struggled to keep up with demand.  They even went so far as to buy up stocks of Red Cedar fences and other things made of Red Cedar to help meet demand for pencils.
• Due to this shortage, Red Cedar is no longer the preferred wood for making pencils with.  Rather, Incense Cedar, that is typically dyed and perfumed to smell like Red Cedar, is used.
• The idea to attach an eraser to a pencil wasn’t thought up until the mid-19th century.  The first patent for such a pencil with eraser attached was granted to Hymen Lipman, in 1858.
• The metal band that attaches the pencil body with an eraser is called a “ferrule”.
• How the cores are placed into wood pencils is as follows:  An Incense Cedar plank is cut with several long parallel grooves.  The core is then inserted into the grooves.  A separate Incense Cedar plank is then glued to the top of this first plank.  The combined planks with the core inside are then cut into pencil size, varnished, and then painted.  Finally, the erasers are added, as well as any text to be imprinted on the pencil.
• John Steinbeck, a known pencil-ite, used over 300 pencils to write East of Eden.  During his peak writing times, he was also known to go through up to 60 pencils a day while writing.
• The pencils Johnny Carson frequently played with on the Tonight Show were specially made with erasers at both ends in order to avoid accidents during broadcasts.
• Standard hexagonal #2 pencils are cut to be 7.5 inches long and with a hexagonal height of around 1/4 of an inch.
• The largest pencil ever made was over 76 feet long and cost around $20,000 to make.  It was made by Ashrita Furman in 2007 as a birthday present for Sri Chinmoy.  The pencil weighs 18,000 pounds, with a 4,500 pound core.  Presumably, the world’s biggest pencil sharpener is needed to actually sharpen this pencil.
• The earliest mechanical pencil was found in 1791, aboard a wrecked ship, the HMS Pandora.