Since the use of bibliometric instruments has grown and will continue to grow in the future, the quality, availability, and accessibility of data on publications and citations is of tantamount importance. But equally important is a correct use of the data. This means that an important task of the bibliometric field is to highlight not only what bibliometric instruments can do, but also what they cannot do. With the increasing call on bibliometrics to evaluate the research performance of individual researchers, teams, labs, institutions and universities, regions, countries, fields, and so on, it is fair to carefully assess the instrument. Evaluating the bibliometric instrument requires first identifying what has to be delivered. In this article, the author describes the research evaluation objective of bibliometrics. Then the author provides an exercise using bibliometrics for the study of scientific disciplines. The author stresses that each bibliometrician should be involved and concerned about discussing and documenting the validity of bibliometric instruments. (Contains 3 footnotes.)