[R0b0t1]

If you look into the sources this is measured by the reading tests you get that present an article and ask questions about it. There is an example in this comment: https://news.ycombinator.com/item?id=29731528

The goals they list on e.g. https://en.wikipedia.org/wiki/Functional_illiteracy match exactly what I was told I was being tested on when I was taking the standardized tests in school.

Roughly, there are these breaks in understanding: 1. Understanding the literal words on the page, 2. understanding the implied context of the words, and 3. understanding the motivations of the author. Progressing in order of difficulty. As well there are ways to gauge how well you can read and how fast you can read, such as are you able to sound out and break down complicated words based on their roots or do you remember whole words.