Elementary question: When one talks of a wave function of a measured object collapsing or decohering or splitting (pick your interpretation), what we base everything on is the measuring pointer. So, which of the following is the case? (a) one calculates with help of coupling constants etc. what wave function of the measured object must correspond to the definite state of the measuring object, or (b) wave function of the measured object is just shorthand for "the wave form of the measuring device" ? Thanks.