Last week, I wrote about how mobs might be predictable. One of the first tools that I mentioned was autocorrelation. This is a basic tool that we will use with the others in the list, so it's important to understand exactly what it does. That's what I want to explore this week.

**Geometry**

Let's go back to high school geometry. We can define several properties and operations in terms of the angles and sides of the parallelogram to the right, though we'll need to dive into the cartesian coordinate system a bit to see how to move on to the next step towards the autocorrelation.

We want to look at what it means to do mathematical operations on these line segments. We know that we can add numbers together to get new numbers, but what does it mean to add line segments? If we take the segment from D to E, and add the segment from E to B, it's obvious that we end up with the segment from D to B. But what's not as obvious is that if we take D to E and add from E to C, we end up with D to C.