What separates the Anthologiae from the other surviving Hellenistic astrological literature is that it shows the work being done. Valens states a technique, then puts charts under it, and there are more than a hundred of them across the books. Some are worked through to a conclusion, some are used to make a single point, and several appear more than once under different methods. The book is closer to a teacher's casebook than to a systematic exposition, and it is repetitive and disordered in the way a casebook is.
The charts are also datable. Because Valens gives planetary positions, modern scholars have been able to compute the moments they describe, which fixes the period he was working in and provides an external check on the text. That is unusually good evidence for an ancient technical work, and it is why the Anthologiae has become the anchor for reconstructing what second century practice actually was rather than what its theorists said it should be. Valens is also present as a person in a way ancient technical authors rarely are. He writes about the expense and difficulty of the study, warns off readers who want it cheaply, and states plainly the fatalism he draws from the art, which he treats as its hardest and most necessary lesson.