Thanks for that - I'll fix the errors you've listed. I know how to use its and it's, and I've proof-read the book several times, but there's still a good bit of stuff like this that I've missed.

It turns out that it's really difficult to proof-read large blocks of text that you've written yourself :/ When your brain sees something it recognises it tends to speed up and skip over bits, seeing what it wants to see, thus missing stuff like this.