I didn't learn much from reading this article. Questions linger in my mind, for example: What are the CIE XYZ coordinates of each colored square? What is the spectral distribution of each square? How were the colors chosen?

These are great, even for manually-adjusted color workflows.

Fun fact, though: You have to replace them every couple of years (or sooner) because no pigment/dye is stable, especially if exposed to bright light.

Having a test shot with one of these in it saves you untold amounts of pain later.