When you're done...
You should see a plot, showing the points in clusters, something like this:
I've put colored boxes around the clusters of points, to make them more visible. The measurements show that the sizes of Phacops do cluster into groups, just as we'd predict if trilobites are really arthropods.
This is a level of detail that many people don't know is in the fossil record. But now you do, because you've actually done it!