I immediately recognized it as the sinc function. It's a function that is extremely important in digital signal processing, and one that I see just about every day I'm in the lab. The sinc function is defined as:

In the case of the picture above,

*r*is equal to:
and therefore, sinc(

*r*) is equal to:
This is the partially obscured equation that you see in the picture. I noticed there was a bit of confusion about this equation in the comment section of IFLS, so I thought I'd clear a few things up.

Many people assumed that the formula written on the front is incorrect. They noticed that plotting a function with

*x*,*y*, and*z*variables would require a 4-dimensions. While that is true, it doesn't mean that the function is incorrect as written. The function is still correct**the***as long as**z*is defined as a variable that is not connected to the cartesian (*x*,*y*,*z*) coordinate system. In other words,*z*could be a time dependent variable or even a constant. When*z*= 0, the plot will look like this:
Which looks like the plot from the picture on IFLS. When we let

*z*vary between 1 and 100 you can get a time dependent plot that looks like this:
This is a good example of why it's important to define your variables

*.*If you don't define your variables they could mean anything. A variable can*look*familiar and mean something completely different. In this case,*z*is not the Cartesian coordinate*z*that you're used to seeing. Remember, a variable means nothing until you've defined it.*c*does not always mean the speed of light,*r*does not always mean radius, and so on.**Now to the fun part!**

I used matlab to make a printable version of this craft. I suggest you print these pictures out on cardstock or the paper will droop down. Print each of the pictures (in order) and have fun putting them together!

**and I'll post it for everyone to see.**

*Send me a picture of your finished product*
(If I get at least 5 submitted pictures I'll post pictures of the sad attempt that my 6 year old and I made)

Aaaaaannnnnnd GO!

*x*axis is where you should cut to place the cross sections you already cut out. This way the sinc(

*r*) wave will be equally spaced in both directions (if you don't use this you could get an oval instead of a circle).