Any type of scientific study or evaluation of research quality and impact enters into two types of problems if there is more than one topic area involved in the study: (1) How to account for differences in (paper) production? (2) How to account for differences in citation impact, i.e. influence over subsequent literature? This paper aims to show that these questions can be answered with the help of two methods; the Field Adjusted Production (FAP) indicator and a percentile indicator which is designed to include the FAP. Consequently, they are used in combination in order to express a score that includes both paper production an impact into one figure. Thereby is constructed a score that can be used for ranking of universities, departments, individuals. The paper first explains the background of the method, and then how to calculate the indicators belonging to the P-Model. Then the paper indicates some examples and will discuss methods for validation of the proposed indicator.