Citation count is one of the easiest and most popular ways of quantifying an article's impact, however, due to different cultures of publishing, this metric (like many others) should be normalized or field-weighted. While a simple calculation in theory (the citation count of a publication divided by the average citation count of all publications of the same type, in the same field, published int he same year), the mass amount of information required to do this is the biggest barrier.
Field-weighted Citation Impact is a normalized citation metric generated by SciVal which is calculated by dividing the actual number of citations received by the average number of citations in that subject area. Taking the discipline of research into account allows for cross-subject comparison of papers, researchers, and even institutions.