Lance reading evaluation system is a set of algorithms developed by Metametircs Education Company with the support of National Institution of Health Institute after 15 years' research. In the United States, Lance reading evaluation system is one of many reading evaluation systems, and it is also the most widely used one. Lance index can help parents and teachers to evaluate and predict children's needs to improve their reading ability from kindergarten to college or after work.

The blue thinking system mainly measures the difficulty of books from two dimensions: semantics and syntactic complexity. Semantic difficulty: the higher the frequency of a word in reading, that is, the more common it is, the more familiar the reader will be and the lower the corresponding reading difficulty will be; On the contrary, the fewer common words readers encounter in reading, the more difficult it is to read. Syntactic difficulty: The longer the sentence, the higher the difficulty. Because there are many clauses in long sentences, readers should not only receive more information, but also deal with more complicated sentence relationships, and at the same time have better short-term memory ability. Therefore, the longer the sentence, the higher the level of blue thinking; On the contrary, the shorter the sentence, the lower the rank of lance.