I've been looking for a low cost option to calibrate my lenses. Photography is an expensive undertaking and I bristled at having to spend another $20 for a hunk of plastic to calibrate my lenses with. Of course, I could've made my own but that wasn't appealing to me either. Amazon had a set of paper cards for $5 to calibrate so I decided to bite the bullet and order them. I'm happy to say my lenses are calibrated.
The cards are artistic in their own way.