From the dotting of an 'i' to the crossing of a 't', each flourish, each connection, each minute aspect of our handwriting is a clue to our personality. What's in a Letter? is an entertaining, interactive kit that includes all the necessary tools for analyzing handwriting.
Is there an "authoritative" text on this subject? I love the way this book has been set out - it's simple and easy to understand. In fact, it comes with a little stencil so that you can see what is meant by "large" or "small" writing as well as to see by what degree it's slanted (either to the left or to the right). But once you've seen a certain letter interpreted in a certain way and then compare it to another book's interpretation, you wonder what to base all the theories on. Some things are obvious, i.e. the slant could well depend on whether or not the writer is left or right handed. It's when you go into the realm of the person's private life (e.g. lack of confidence, sexual relationships, etc.) that there's a fair amount of conjecture. I've sent one or two of the cards in this kit as a member of Postcrossing: