Quantitative phenomena can be displayed effectively in a variety of ways, but to do so requires an understanding of both the structure of the phenomena and the limitations of candidate display formats. This paper recounts: three historic instances of the vital role data displays played in important discoveries; provides three levels of information which form the basis of a theory of display to help us better measure both display quality and human graphicacy; and describes three steps to improve the quality of tabular presentation. (23pp.)