An effective user manual is, first and foremost, one that gets read. Secondly, it is a manual that actually helps its readers. rtfm* shows you how to figure out what to write about, how to organize the material you've selected, and how to write it (including the grammar rules you learned in school that you should ignore). You'll even learn the basic rules on how to lay out your pages to support readers looking for information. And, like any good user manual, it's only as long as it needs to be.
The idea of the book is good but the almost 90% of my book (in kindle format) does not have a proper apostrophe (') in place which is weird for the book talking about how to write. It is just missed from where it should be, for example, "you re" instead of "you're". I can found it from the beginning to the 50% of the book then it looks good until the 60% of the book that the missing is back.