This is 99% invisible. I'm Roman Mars.

Whether or not you're a fan of math, it's undeniable that as a society we've always had a need to count things.

Maybe it's to figure out the maximum weight an airplane can safely hold,

or the appropriate amount to tip after a meal,

or the exact number of minutes in a year so that you can... a track of numbers has always been a part of what makes us human. So at some point

along the way we created a tool to help us keep count and then we gave that tool a

name. We called it a calculator. But depending on what era you were born in and maybe even what country, what constituted a calculator varied widely.

In elementary school, I had a calculator watch, which I thought was the coolest thing in the world.

When I visited my dad's house, I would marvel at the slide rolls that he had in his junk drawer.

His father, a bookkeeper, had a monstrous metal adding machine in his office that I used to love to play with.

And if you go back far enough to a time before written numbers even existed,

a calculator was also an abacus, a tally stick, and our very own fingers and toes.

Regardless of the form it took, though, what's clear is this.

Without the calculator, our built world as we know it just would not exist.

You trace it all the way back and it's like, oh, the entire recorded history of humanity is kind of driven by the fact that we have to count things.

This is author Keith Houston. He writes all about the evolution of the calculator in his new book.

My name is Keith Houston, and I am the author of Empire of the Sum,

The Rise and Rain of the pocket calculator.

Well, let's talk about this need for calculation and for counting.

It seems like we, you know, as organisms seem to recognize that we always need to count more than we have the

tools to count.

Let's talk about like, you know, the historical origin of counting and that drive. I think the funny thing is in a sense there's not a

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