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The International Competition for Nerdiest Nerd, Hank has been declared the winner. In this video, we take apart an RC Allen 805 mechanical adding machine and try to figure out how it works. We're mostly unsuccessful, but it's so PRETTY!

Here's the Numberphile video on the Enigma Machine:

Here's where Hank and Katherine and John are playing mario games:

And here's an amazing channel on how various mechanical computers work:

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Good morning John. Today’s Vlogbrothers is going to be a little bit weird. I am right now at an antique mall. I found a thing that I am so amazed by that I just can’t help but take it apart. 

It is now in my home! This thing is at least 25 pounds. It’s made entirely of metal, and it can do addition and subtraction and kind of multiplication. Not really. 

Obviously, a calculator that can do addition and subtraction these days is not impressive. But when it was purchased it probably cost around as much as a really nice laptop today.

I don’t know how this works, but that's what I’m going to try and figure out today. There are a number of amazing things going on all at once inside of this machine.

First, most simply, let's just put in the number 99, that’s 99 cents. Both of the dials will count up to nine. If we add one to the 99 there, if we add one cent, we’re gonna get a buck right? 

Now, I know how the first column happens. There is a pin that tells in the machine that to roll this dial, the first column dial, one digit. Now that makes sense.

But then it gets carried forward and that is amazing to me. What? How did this machine, that is a just a machine, figure that out? 

That's what we wanna know, and as far as I am concerned, there's only one way to find out. So let’s take it apart.


Ugh. What is this? Is it a dead animal? Something crawled in there and died like a thousand years ago? Oh I have no idea. But I touched it.

Now this thing comes off and… I got one of these! I should now be able to lift this off of the mach-- I can! It’s fuzzy on the inside. Oh man. 

Now this just got way cooler! There’s been something rolling around in here. I can hear it. It’s a dime! 

1980, so it’s not that old. How does it stop at the right place? How does it carry the number? How does the subtract function work? 

Nerdy? Yes. Yes, it's nerdy. It is very nerdy. Each one of these parts had to be individually stamped. How do you come off? I hate flat head screws so much right now.

A lot of these screws are really stuck, which is not all that surprising. You actually have to be depressing a button in order to access this screw; so that’s something. Were those the only four screws? Yes! 

Well something’s happened. Whooooaaaaa. Okay. This is the back of the number plate. When you push each of the numbers, it pops down into one of those nine slots there. 

Ah! I got it! I figured it out! When you push down a number, two things happen. One, that depression will push down this lever a little bit, and that actually allows for this thing up here, the gear that actually turns the number wheel, to actually start moving. 

How much it moves is a question of which key got pushed down. Whichever button is pushed will actually block that at a certain point if nothing stops it, it will go all nine, and you get nine. 

If it stops like half way in the middle then it stops at five, and it will only count five.  So this oil I have on my fingers right now was put on here by someone in a factory in the 1930s. The numbers are somehow responsible for the digit carrying. 

Boy, am I glad I didn’t have to manufacture these things for a living. I would have not been good at it. So at zero, this notch holds this pin, and this pin, when you move it out of the way, it just automatically advances. That pin is the secret. 

You know, it’s the kind of thing that we would never make today but it has, in its functionality, a beauty that I am a big fan of. It does so many things all at once, and it is powered only by the crank of the hand. 

Thanks to all the people who, uh, you know, we won't remember the names of who put all their time and energy into the creation of these devices. It’s just so very neat. So very, very neat. 

John, I’ll see you on Tuesday.