Obscurity: this setting controls the rarest word can be picked for both words. Low: 200, Medium: 2000, High: 7000

Difficulty: this setting controls the minimal frequency difference between each word, higher difficult allows more more similarly frequent pairs of words to appear.

These unigram frequencies are sourced from Jun Da, Ph.D., Associate Professor of Linguistics.

They are hosted at https://lingua.mtsu.edu/chinese-computing/statistics/char/search.php