The Equals Sign for Kids: Who Invented It and What It Means

0:00 Welcome to Maths Is Not Boring by kidopoly.com. I'm Mira! And I'm Finn! If you haven't already, tap follow wherever you're listening so you never miss an episode. Okay, Mira, I'm ready. What ordinary thing are we looking at today? We are looking at something so ordinary you probably wrote it down in school today without even thinking about it.

0:23 Like a letter? A number? Two tiny horizontal lines, stacked perfectly on top of each other. Wait, two horizontal lines? Do you mean the equal sign? Exactly, the equal sign. But Finn, I want you to be really honest. When you see an equal sign at the end of a math problem, what do you think it tells you to do?

0:48 Oh, that's easy. It means the answer comes next. It's like a starting gun in a race. That is exactly what almost everyone thinks. We are taught that it's a doorway you walk through to get to the answer. We think it means calculate this now. Wait, are you telling me it doesn't mean that? It doesn't mean that at all.

1:09 What it actually means is so much bigger and so much more beautiful. Wait, it doesn't mean the answer is coming. Then what on earth is it doing? To truly see it, we need to leave today behind. We need to travel back to the year 1557. I love a history trip. Where are we going? We are going to London to meet a brilliant Welsh doctor and mathematician named Robert Record.

1:34 Okay, 1557. I'm picturing cobblestone streets, people riding horses, and Robert sitting at a wooden desk with a feather quill and a pot of darking. You've got the picture exactly right. Robert Record was sitting at that desk, writing a very important math book called The Whetstone of Wit. The Whetstone of Wit?

1:58 That is an absolutely brilliant name for a book. It sounds like a magical object from a fantasy story. It really does. Now, Robert was puzzling over a very practical problem. He was writing out lots and lots of math, but back then there was no symbol for equals at all. No symbol? So how did people know when things matched up?

2:21 Every single time he wanted to show that two amounts were the same, he had to write out the words is equal to by hand. Ugh, writing is equal to over and over again with a scratchy feather pen. That would make my hand cramp so badly. Exactly. He grew incredibly tired of it. It was tedious. He wanted a shortcut.

2:45 He needed a symbol that was quick to write, but also proved that two things were exactly the same. So what did he do? Did he just immediately draw the two little lines we use today? He drew two parallel lines of the exact same length. But they weren't little. His lines were much, much longer than the ones we use today.

3:06 Whoa, so he just drew these giant tracks right in the middle of his sentences. Yes, like two long, straight railway tracks sitting flat on the page. And we know exactly why he chose that specific shape. What did he say? Why those lines? He wrote that he chose the two lines, quote, because no two thingers can be more equal.

3:32 Because no two things can be more equal. Oh, that is so clever! If they are exactly the same length, they are the ultimate picture of fairness. Exactly. And his book was a massive milestone for another reason. It was actually the very first book in the English language to use the plus and minus signs too.

3:54 Wait, hold on. The very first English book to use plus, minus, and he invented the equal sign. That guy practically gave us the whole math toolkit. He really did. But here is the funny part. His beautiful new equal sign was very slow to catch on. People can be so set in their ways. People are so stubborn sometimes.

4:20 It was such a perfect idea. They really are. People kept using other strange symbols, or just writing it out in words, all the way into the 1700s. But let's go back to your first thought, Finn. The idea that equals means, ta-da, the answer is here. Because that's how we still use it today. Yeah, because if I buy an apple for two coins and a pear for three coins, the equals sign comes right before the five coins I have to pay.

4:51 Right. But Robert records giant parallel lines weren't pointing to an answer at all. They were showing a balance. A balance? Like standing on one foot? More like weighing things. I want you to imagine an ancient pair of scales, or a seesaw at the park, held perfectly level. Oh, I'm picturing a bright red seesaw, and nobody is touching the ground.

5:17 It's just hovering right in the middle. Yes, that perfect hover is what the equal sign actually means. Both sides balance exactly. The stuff on the left side is the exact same amount as the stuff on the right side. So it's not a machine that spits out a number. It's just a scale at rest. Precisely! Like if you put a giant heavy pumpkin on the left side of the seesaw, it would tip all the way down.

5:47 And I'd need a whole bunch of smaller apples on the right side to balance it back out perfectly flat. Exactly! The pumpkin looks completely different from the pile of apples. But the equal sign in the middle tells us their total weight is identical. My brain is doing flips right now. Two plus three looks totally different from a plane number five.

6:10 But the equal sign says they have the exact same weight. You got it! That balance sits at the heart of every equation ever written, and every fair swap in history. It just sits there, perfectly peaceful. That is actually really beautiful. It makes math feel completely different. Less like a bossy instruction manual telling me to calculate things.

6:35 Wow, Finn, yes! It is not an instruction. It is a picture of the universe just balancing itself out. I am going to see tiny seesaws everywhere now. Every time I look at a recipe to see how much flour equals how much sugar. Or when you trade playing cards with your friends. If you trade three regular cards for one rare card and everyone is happy, that's an equal sign.

7:02 Every fair swap is an equal sign. Two parallel lines perfectly matched. It's like a secret code hidden in plain sight. It really is. And to think it all started in 1557 with a Welsh doctor who just got tired of writing the same words over and over again. Alright Finn, it is time for the quiz. Are you ready?

7:26 I am so ready. Bring on the seesaws. First question. What was the full name of the Welsh doctor and mathematician who invented the equal sign? Next one. In what year did he publish the book introducing this symbol? Question three. What was the magnificent name of his math book? Here's number four. Instead of meaning the answer comes next, what does the equal sign actually mean?

8:08 Last question. What two other famous math signs did his book use for the first time in English? Great job, let's see how you did. The first answer is Robert Record. For question two, he introduced it in the year 1557. Number three, the answer is the whetstone of wit. Question four. It means both sides balance, just like a perfectly level seesaw.

8:42 And the final answer is the plus and minus signs. I'll never look at a pair of straight lines the same way again. They're like little resting scales. I know. The most ordinary things hold the deepest secrets. If you loved picturing math balancing today, please leave us a five-star review. Just scroll down and tap the stars.

9:05 And follow us right here so you never miss an episode. Oh, and we have sister shows too. History, science, and philosophies not boring. Go give those a listen and a follow as well. And if you want a shout out on the show, or just want to say hi, email us at hello at kidopoly.com. See you next time on Maths Is Not Boring.

9:28 Bye everyone.