The Rotation tab lets you set the rotation angle increment for the F8 key and constrain rotations to angle increments for manual rotation. To change the rotation units setting (degrees or radians), click the Rotation Angle Units button and choose the new unit. Click Options from the Tools menu to open the Options dialog box.
Setting the F8 Rotation Increment
You can change the F8 rotation increment by clicking the arrows beside the F8 Rotation Increment box, entering a new value, or dragging the red needle in the dial control.
Setting a Manual Rotation Increment
Setting Manual Rotation Increment to a non-zero value, constrains manual rotation to increments of the specified value. For example, if you set the rotation angle to 12 degrees, an object rotates in increments of 12 degrees when you drag its corner rotation handles. To change the Manual Rotation Increment, enter a new value or drag the red needle in the dial control.