Oh, I'm a hardware engineer by trade. But I'd forgotten how to find the angle between to vectors. I just typed in "angle between two vectors" into google and get several hits. The rest of it is fairly simple algebra although since the formula syntax is a subset of C, it helps to know C. When I first read the Carrara manual, I blew off formulas but I've since come to find them very useful. I wish there was a way to use one as an operator, i.e., have it operate on underlying data. Then you could do some really cool stuff. Marc