To say that the most famous model of pencils, it is the 2B pencil.
From the day I started painting answer cards, the 2B Pencil stood out from the crowd of pencil models and was stationed in our stationery bag. Before holding the big and small exams, the class teacher would always emphasize over and over again on the podium that it was necessary to use 2B pencils and 2B pencils. Even when waiting for the exam, the invigilator will come up to you and point to the pencil, look at you, and ask, "Is it 2B?" Well, it's too hard to answer.
<h1 toutiao-origin="h3" >, why are 2B pencils so special? Is it a special pen for exams? </h1>
To understand why 2B pencils are so special, we have to understand the grading system for pencils and pencils.
Perhaps unexpectedly, the pencils we usually use are not made of lead, but of graphite and clay. We call it a pencil because in ancient times, human beings had the habit of using lead powder to record, and in 1564, when people discovered graphite, they mistakenly thought that it was a kind of lead. Because both graphite and lead can be used for records, people call graphite "black lead", and with the interest in trade, a business name is "pencil and pencil". Over the past hundred years, the name of the pencil has become a habit.
Because the proportions of graphite and clay are different, pencils also have a corresponding grading system. In order to ensure that everyone can buy the right pencil, it is stipulated that H (hard) represents hardness and B(black) represents blackness, which is divided according to the amount of graphite in the refill. The larger the number in front of H, the harder its lead core is and the lighter the color. The larger the number in front of B, the softer the lead core and the darker the color. In daily life, "number + H" generally means a hard pencil, "number + B" means a soft pencil, "HB" means a pencil with moderate soft and hardness, and "F" means a pencil with a hardness between HB and H.
It is reasonable to say that the HB pencil is moderately soft and hard and black, it should be the most suitable pencil for writing, why not use HB, but use 2B? This has to talk about another great (gai) big (si) invention - the cursor reader (
Because the general machine-readable card is judged according to the pencil graphite concentration and the size of the area of the blackened area, H series pencils with too little graphite concentration and B, HB, F pencils are excluded. Larger than the 2B series pencil, the graphite concentration is enough, but because of the hardness, it is easy to blend and pollute other answer cards; coupled with the difficulty of painting, it is easy to cause misjudgment, and the falling graphite chips will even make the cursor reader malfunction, so it is not the most ideal choice.
While the 2B pencil is great for scribbling answer cards, for engineers or architects, the wear-resistant and hard H Series pencils are a good companion for work. The soft but black B series pencils are an indispensable tool for artists to draw with light and shadow. What kind of pencil to choose, mainly depends on the use.