Materials:

- A hand.

Here are Tara's Three Rules for counting in binary on your hands.

1. When a finger is down, that is '0'.

2. When a finger is up, that is '1.'

3. Do not count your thumb.

In this picture, all fingers are down. So this means zero.

You maybe wondering why the thumb is out.

The answer is that it does not matter where the thumb is. I do not count the thumb when counting in binary. When we get to number 10, you will see why I leave the thumb out.

Let us add 1.

### Teacher Notes

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## Step 1: One

This is 1.

Put the index finger up.

1 finger is up, so this is the binary number 1.

## Step 2: 10

Read the fingers from left to right. The middle finger is up, so that is 1. The index finger is down, so that is zero.

This makes the number 10.

This number is why I leave my thumb out when counting in binary. I started doing that when a teacher thought I was flicking her off. She was not impressed when I said, "I am not flicking you off, I am counting in binary.

## Step 3: 11

Read the fingers from left to right.

You get the number 11.

## Step 4: 100

This is hard to do because my ring finger is not flexible.

## Step 5: 101

Ring up, middle down, ring up is 101 in binary.

## Step 6: 110

Ring up, middle up, index down is

110.

## Step 7: 111

Ring up, middle up, and index up means the number is 111.

## Step 8: 1000 Through 1111

Here are the next 8 binary numbers. Can you read them?

If you can, congratulations! You have learned to count up in binary!

## 3 Discussions

2 years ago

By excluding the thumb, and leaving it to stick out instead, you can only count half as high. When you account for both hands, you can only count a quarter as high as you could by using your thumbs. If you are worried about how people will take 0010000100, you can use the simple expedient of reversing your hands, facing your palm away from you, and beginning at the pinky instead of the thumb.

3 years ago

how we know we read correct figures as u mentioned last 8

5 years ago on Introduction

Cool trick! Thanks for posting!