avl-tree

I'm looking for the best way to calculate a nodes balance in an AVL-tree . I thought I had it working, but after some heavy inserting/updating I can see that it's not working correct (at all). This is kind of a two-part question, the first part would be how to calculate the height of a sub-tree, I know the definition "The height of a node is the length of the longest downward path to a leaf from that node." and I understand it, but I fail at implementing it. And to confuse me further this quote can be found on wikipedia on tree-heights "Conventionally, the value -1 corresponds to a subtree

Can someone please explain what the main differences between these two data structures are? I've been trying to find a source online that highlights the differences/similarities, but I haven't found anything too informative. In what cases would one be preferred over the other? What practical situations make one "better" to use than the other? AVL trees maintain a more rigid balance than red-black trees. The path from the root to the deepest leaf in an AVL tree is at most ~1.44 lg(n+2), while in red black trees it's at most ~2 lg (n+1). As a result, lookup in an AVL tree is typically faster,