Stewer, I understand. As a programmer who has dealt with 3D graphics programming, I know all about Euler angles, order of rotation, and gimbal lock. Because quaternions aren't dependent on the "order of rotation" (and therefore don't suffer the gimbal lock problem), they are the best choice. Not the most understandable, but the best. As I said, there are ways to convert between Euler angles and quaternions, so the interface doesn't matter. You can specify Euler angles in the interface and convert to quaternions for the actual rotation in order to avoid gimbal lock. As for "trackball" rotation, there is a full algorithm developed by Ken Shoemake that allows full rotation without gimbal lock. I've heard that it requires a little practice as it is not entirely intuitive. Mason makes a good point (that others have made also) that CL probably didn't incorporate quaternions because it just isn't a necessity - and maybe too much work ;). Other 3D apps, like 3DSMax, have a work around for gimbal lock and as stewer mentioned, still use Euler angles. On the other hand, many games use quaternions (at least from what I've read).