1. He made sure he wore T-shirts and underwear in proper rotation . 2. In addition to preserving length, proper rotations must also preserve orientation. 3. The matrices corresponding to proper rotations ( without reflection ) have determinant + 1. 4. Matrices of all proper rotations form the special orthogonal group. 5. But by insisting on determinant + 1, we can restrict the matrices to proper rotations . 6. By convention, the axis of proper rotation of greatest order is defined as the principal axis. 7. Proper rotation to get true flight of ball.8. For proper rotations , this is the axis of rotation and the points are fixed by the rotation. 9. The discussion so far only relates to proper rotations , i . e . rotations about an axis. 10. Each of these groups has a subgroup of transformations which preserve proper rotations and pure translations ).