Understand readability scores
Each readability test bases its rating on the average number of syllables per word and words per sentence. The following sections explain how each test scores your file's readability.
This test rates text on a 100-point scale. The higher the score, the easier it is to understand the document. For most standard files, you want the score to be between 60 and 70.
from https://support.office.com/en-us/article/Test-your-document-s-readability-85b4969e-e80a-4777-8dd3-f7fc3c8b3fd2#__toc342546555
- Flesch Reading Ease. This score rates the readability of your text on a 100-point scale, with higher scores being easier to read. Scores from 0-60 are typically regarded as college or college graduate level and fairly difficult to read. Scores from 60-80 are regarded as reasonably easy to read and written in plain English. Most professional documents fall into this range. Higher scores than 80 are regarded as easy to read for kids.
- Flesch-Kincaid Grade Level. This scores rates the readability of text based on U.S. school grade levels. A score of 4.0, for example, means writing that can be understood by a fourth grader. Most professional documents fall somewhere in the range of 7.0-11.0.
from https://www.howtogeek.com/247921/how-to-test-the-readability-of-your-writing-in-microsoft-word-or-outlook/