A graph is an example of a symbol system which encodes information through the juxtaposition of marks in a two dimensional plane; decoding the meaning of a graph uses specific attributes of the human visual system. This study was undertaken to identify some variables critical to graph interpretation as a first step in designing better curriculum materials and methods of instruction. The study was developed to define and investigate the differences between novice and expert graph readers on the dimensions of average fixation duration, percent of total viewing time, and performance on a selection and memory task. Results indicated that the experience of the graph reader played a major role in the interpretation process by signaling the need for the cognitive decision to increase fixation duration in important blocks of the graph. The mathematical graphs used in the study tended to draw experts' as well as novices' eyes to the important information. (TW)