During the last five years much work has been done in developing the spreading resistance technique. This work has led to a much clearer understanding of the strengths and weaknesses of the technique. It has been shown that it is capable of producing carrier concentration profiles which are accurate enough to be used in process control and development. A review is presented which highlights the three steps necessary to obtain such data. These are the optimization of the acquisition of raw data, the conversion of the raw data to carrier profiles, and finally the interpretation and use of the final profiles. A great emphasis is placed on the need to acquire the most accurate and reproducible data and on the methods which are used to achieve this objective. For the accurate profiling of ultrashallow layers such procedures are shown to be of paramount importance.