The writing process

I'm into almost the last week of writing The Universal Machine and I've been asked about my writing process. So here, in general terms, is how I have approached the writing.
    For each chapter I've thought about a general idea of what I want to include and eventually I sketch this down as a rough outline or plan. During this time I'll be reading books about the subject material and using online reference sources. If it's a book I'll use those Post-It tabs to mark pages with useful content on. If its on online resource I use Evernote to clip parts of it. Then once the reading is finished I'll start writing using the marked parts of the books and Evernote as my reference sources. Wikipedia is used to check facts and add details. It's great for facts but very poor for adding colour which has to come from biographies or first-hand recollections. Once a chapter is written I'll put it to bed and move on to something else. Then, I'll return and read/edit the chapter several times. Once I'm reasonably happy with the chapter it is emailed to a good friend who is a professional writer. He reads and picks up mistakes and makes suggestions for improvements. Each chapter is also sent out to one or more academics/specialists with an interest in computer history or specific subject areas to check the factual content and identify potential omissions.
    All of the returned chapters are edited to take into account the feedback and the chapters are then reread and edited over and over. I estimate that most chapters have been reread and edited at least a dozen times. I've been working on this over a year now and  I'll be sad when I finally package it up and send it to my publisher. I've had a great time writing this.