I wouldn't use it, but I guess you could waste time messing with it. . .You should add like:
Inches - Feet - Km - Miles
To where it would be like. . .you enter 6 inches and it says its 50% of a foot and whatever % it is in the rest. That I would use. But also this one is huge! theres tons of space there, I like my stuff as compact as possible. Then adding a "On Top" check box would be helpful, so it'll be the top window.
But the book pages. . .I don't think many people would actually use it.