the bubbles completely, and then reminded that -- for reasons that no one ever explains

完全塗滿答案格，並被提醒只能使用 2 號鉛筆

-- you can only use a number 2 pencil!

而且也沒有告訴你為什麼！

Now, unless you're an artist, you've probably never even seen a pencil that's not number 2,

現在，除非你是個藝術家，你可能從來都沒有看過 2 號以外的鉛筆

also known as an HB pencil outside the U.S.

2 號鉛筆在美國以外的國家稱作 HB 鉛筆

The thing is, if you used any other kind of pencil when you took an automatically-scored test,

其實，如果你在考電腦閱卷的考試時，使用其他類型的鉛筆

you'd probably be fine.

可能也沒關係

However there are reasons that test instructors still tell you to stick to number 2.

然而，考試仍然規定你只能使用 2 號鉛筆是有原因的

And they have a lot to do with how machines score your tests -- or at least, how they used to.

因為這跟電腦閱卷機器的閱卷方式有關──或者至少過去是這樣

In 1931, a high school physics teacher named Reynold Johnson was grading exams

在 1931 年，一個名叫 Reynold Johnson 的高中物理老師在改考卷

when he wondered if there might be a way to score them without actually having to go through

他開始思考是否有別的辦法可以不用親自閱卷

every single answer by hand.

就能打分數

He knew that graphite, the writing material in pencils, was electrically conductive.

他知道鉛筆書寫的原料「石墨」可以導電

It's made of flat sheets of carbon, and its outer electrons are relatively free to move around

它是由碳原子平面層所組成，且其外層電子可以相對自由地

within the material.

在物質裡流動

So Johnson devised a machine with many small electrical circuits that would pass over an answer sheet.

所以 Johnson 發明了一台裡面有許多小電路的機器，可以審閱答案卷

If there was a pencil mark on the sheet, it would conduct electricity through

如果有答案欄上有鉛筆畫記痕跡，將會透過其中一個電路導電

one of the circuits, and the machine could record it as an answer.

而後機器可以將其記錄為答案

Eventually, he sold the idea to IBM, which produced the first mark-sensing machine.

最後，他把點子賣給了 IBM，製造出第一個能偵測鉛筆畫記的機器

But the number 2 thing didn't become an issue until the next generation of machines were introduced in the 1960s and 70s.

但是 2 號鉛筆直到第二代機器在 1960 到1970 年代被發明後才受到重視

Those machines had light-sensing devices called phototubes, and if they did not detect light

那些機器裡有叫做光電管的光感測設備，如果在某個點沒有偵測到光

in a certain spot, they recorded it as an answer.

它就會被記錄為答案

That made graphite especially useful, because it's better at blocking light than many inks.

這使得石墨特別有用，因為它阻斷光的效果比其他油墨更好

Graphite reflects most light -- that's why pencil marks are so shiny -- and absorbs the rest,

石墨反射了大多數的光，並且吸收其他的光，這就是鉛筆痕跡如此閃亮的因素

which is why it's black.

使得鉛筆痕跡很黑

But for a long time, these optical mark-sensing machines were very picky.

但有很長一段時間，這些光學標記感應機器是很挑剔的

And that's where the different grades of pencil came in.

而這也正是不同硬度鉛筆出場的原因

The graphite in pencils is held together by clay, so manufacturers can control how soft

鉛筆的石墨是由黏土結合在一起，因此製造商可以控制

or hard it is, and also how dark it is. The softer the graphite, the darker the pencil's mark.

軟硬及深淺程度。石墨越軟，鉛筆畫記越黑

Pencils are labeled accordingly.

鉛筆具有相應的深淺程度標記

In the United States, those labels are numbers. International manufacturers use a different system,

在美國，那些標記用數字表示。國際製造商使用不同的系統

with HB corresponding to number 2.

就像 HB 就等於 2 號

Number 2 pencils make marks that are just dark enough to be sensed by the machine,

2 號鉛筆讓畫記夠黑，足以被機器偵測

but also light enough to be erased without leaving a readable mark.

但也能輕鬆地被擦掉，不留下會被偵測到的殘留痕跡

These days, scoring machines use much more advanced sensors that can detect almost any

近來，閱卷機器使用更先進的感應器，幾乎可以檢測

sort of marks you make, as long as they're in the bubbles.

所有形式的畫記，只要它們在答案框裡

So you could probably take your next exam with any kind of pencil you wanted.

所以下次考試你可以試著用任何一種你想用的鉛筆來作答

But your SATs probably aren't the time to test that hypothesis.

但是，你的 SAT 測驗可能不是驗證這個假設的好時機

Maybe bring a couple of number 2s just to be safe.

或許可以帶一些 2 號鉛筆以防萬一

Thanks for asking, and thanks especially to all of our supporters on Patreon, where,

感謝發問，並特別感謝所有 Patreon 的支持者

if you support us at four dollars per month or more, you can submit your questions to be

如果你願意用一個月四塊錢來支持我們，你可以傳給我們你的問題

answered right here on SciShow Quick Questions. And if you want to keep getting smarter with us,

並由 SciShow Quick Questions 幫你解答。如果你想要和我們一起變聰明

don't forget to go to youtube.com/scishow, and subscribe.

別忘了訂閱 youtube.com/scishow