The Dale Chall readability formula is a readability test that provides a numeric gauge of the comprehension difficulty that readers come upon when reading a text.
The mathematical formula uses the parameters of average sentence length and percentage of difficult words as inputs. A word is considered difficult if it does not appear in a revised standardized list of 3000 words that groups of fourth-grade American students could reliably understand.
Additional detailed information on AutoCrit’s readability statistics can be found here.