Difference in rotation without gimbal lock

Ina - this is exactly what quaternions are for.

check out the quat. manual page for all your options.

you can only multiply quaternions.. is it possible to find the change in angle between frame 1 and frame 2? if you have two different quaternions, one from frame1 and one from frame2, how do you find the difference in angle between them?

This might be usefull: http://docs.unity3d.com/Documentation/ScriptReference/Quaternion.Angle.html

and http://docs.unity3d.com/Documentation/ScriptReference/Quaternion-eulerAngles.html

.Angle as zyzyzyzyx says !

indeed,

Documentation/ScriptReference/Quaternion.SetFromToRotation.html

will build you a quat, based on the previous and new heading (Vector3) of the item!