As a running log of a test the Stress-strain diagram inherently supplies both a quantitative and a qualitative record of the mean response of a specimen to load. Stress-strain diagrams have been used almost exclusively, however, fro evaluating the constants)for classic strength, stiffness, etc.) ordinarily used in design, but they rarely have been used for their qualitative indications as evidenced by their shape, or as a basis for possible study of the phenomena of failure. This bulletin presents a percentage technique which offers a simple means for study and comparison of shapes of stress-strain diagrams regardless of quantitative differences. The bulletin supplies illustrative comparisons quantitatively, through the percentage diagram, for the stress-strain behavior of steels and steel alloys, non-ferrous metals, timber, portland cement, plaster of Paris, concrete and stone. The use of percentage diagrams to compare the behavior of materials in tension, compression, flexure and torsion and to compare lateral and longitudinal stress-strain behavior is illustrated. The limited data reported in this bulletin indicate that within one on general class of materials (such as timber, concrete or stone) variables which produce great differences in strength, stiffness and other properties, resulting in a wide variety of conventional stress-strain diagrams, may have no discernible effect on the qualitative stress-strain behavior (as indicated by the virtual coincidence of the percentage diagrams). Other variables which may or may not greatly affect the properties of the material often show pronounced qualitative or shape effects on the diagram. Because it can be used to separate the qualitative symptoms from those which are primarily quantitative, the percentage technique constitutes a useful tool for exploration of the break-down process, contributing thereby to the better understanding of engineering materials that promote improvement and more intelligent use.