The first four chapters of the book are sealed, and ready for printing. Spell checking, re-reading, removing overfull \hbox (you don't know what an overfull \hbox is? You haven't lived! :-) ), re-reading, etc. Then there are the diagrams: move that box left a mm, un- bold that word, align the caption, highlight the arrow. A huge amount of last- moment changes and tweaks. Nothing serious mind you, but a lot of work nevertheless. Four chapters down. Twenty to go. And eight appendices (appendixes).