I just wanted to get a rough idea on how different Chinese writers compare with each other in terms of accessibility for foreign language learners. As a native speaker, I'm not in a good position to assess the relative ease or difficulty of a book. Of course I know 《道德经》 is more difficult than 《小布头奇遇记》. But what about normal books that normal people read? I wanted a more objective criterion. And I think I've found one – the number of unique characters in a book. (Total characters and unique words are also useful – Chinese word segmentation is not a perfect science but the number still means something when comparing different texts.)