How was the 2B pencil, the "official" pencil for the college entrance examination, selected?

Whenever the word "college entrance examination" is mentioned, I can always think of that summer, the building that didn't finish shouting, the people who didn't have time to say goodbye, and the "2B pencil" that the teacher kept talking about. Why did the "2B pencil" stand out from the many college entrance examination elements? Today, Pang Ke will take everyone to talk about the story.

1.What is a “2B pencil”?

Before we figure out this question, we must first make one thing clear: there is really no lead in the pencil! It is made of graphite and clay. The commercial term for graphite is "pencil lead", but in fact it is not lead, but a mineral. It is composed of carbon, gray-black, lubricating and plastic. It can be used to make crucibles, electrodes, pencil leads, lubricants, pigments, etc. Graphite and lead have one thing in common, both can draw black marks on paper. Therefore, people also call graphite "black lead", and pencils get their name from this.

After talking about pencils, let’s talk about “2B”~

I wonder if you have ever noticed the meaning of the letters "H" and "B" on pencils. In fact, according to the different mixing ratios of graphite and clay, pencils also have a corresponding grading system, and these letters are the symbols for distinguishing them.

Among them, H (hard) represents hardness, B (black) represents blackness, "number + H": the larger the number, the harder the pencil is, and the lighter the color of the words written. "Number + B": the larger the number, the softer the lead of the pencil, and the darker the color of the words written. "HB": represents a pencil with moderate hardness. "F": represents a pencil with a hardness between HB and H.

So "2B" is used to indicate the hardness and blackness of this pencil.

2. There are so many types, why did you choose 2B pencil?

In order to solve this problem, we must first understand the "cursor reading machine (commonly known as the marking machine)".

OMR is a computer peripheral input device that integrates optics, mechanics and electronics. Its function is to identify the written content on the information card.

There are some rectangular marking areas with scribbled information printed at specific locations on the information card (think about the location of multiple-choice questions on the answer sheet, it is that place). Use a pencil to fill in the small square mark black, and the photoelectric conversion component of the cursor reader can recognize the filled-in information through the reflection or projection ability of the information card, and convert it into electrical signals and transmit it to the computer for processing.

Its core part is the photoelectric sensor, also known as the photoelectric reading head. Its basic principle is that the light emitted by the light-emitting device is irradiated on the information position of the information card (infrared sensing graphite technology). If the information position is painted black, part of the light is absorbed and the reflected light becomes weaker. Otherwise, the reflected light becomes stronger. The corresponding receiving tube (referred to as the photosensitive tube) converts the light signals of different strengths into analog electrical signals. After conversion, digital filtering and pattern recognition, the detection of filled and unfilled information positions on the information card is completed.

The infrared induction graphite technology detects two indicators of the painted color block: carbon concentration and area (designed according to the information input into the computer and in accordance with the format required by the design specifications of the cursor reader. Circles and crosses are not standardized filling methods). Only when these two indicators meet the standards at the same time will it be recognized as a valid mark. Therefore, if the graphite concentration is too low, it may cause the test to fail due to insufficient carbon content. H series pencils and B, HB, and F pencils are thus excluded.

The graphite concentration of pencils larger than 2B series is too high. During the exam, it is difficult to erase and change the answer. Moreover, the high content of graphite can easily attach the paper to other candidates' answer sheets, which may affect other people's scores. Therefore, these pencils are passed. After such a test, only 2B pencils can take on this task!

Therefore, not only in the college entrance examination, but also in all the large and small exams in our student life, the presence of "2B pencil" has never disappointed anyone~ Speaking of this, Pangke would like to give another warm reminder: friends who take the exam must go to regular places to buy examination supplies. There are many counterfeit and shoddy products circulating in the market nowadays, so be sure to buy regular brand products!

Finally, Pangke wishes everyone in advance that you will win the first prize and have your name inscribed on the Wild Goose Pagoda! Victory will definitely belong to you~

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