The formal validity of an argument can be tested by algorithms described in texts on formal logic. It may even be possible to develop combined syntax and grammar checkers that scan documents written in a mixture of formal and natural languages. Perhaps checking the grammar of documents in a software project could help the developers do a better job by ensuring that the documents are more readable and less ambiguous. This short note has no space to discuss the pros and cons of using graphics and tables in computer documentation. I believe that we can and should develop documents that have parts that can be viewed in many different ways.
Some research suggests that a book-like format works well.
It is again easy to develop or find tools that aid structure and also generate lists and indexes automatically. We could prepare a concordance of each document and make sure that all the words that are used infrequently in the document are indexed and defined. Last and Best I have left the most accurate way of assessing the understandability of documents until last. It has been used for many years on many successful software projects. To assess the qualities of a document get a collection of people to read it and report on it.