The reliability of data derived from any stress-strain diagram is dependent upon the accuracy of the strain instrumentation and related accessories, as well as the testing machine itself. That is why Tinius Olsen places such emphasis on the accuracy of all equipment - not just enough to pass minimum standards, but accuracy that exceeds ASTM and other applicable specifications. In this way, you can be assured of optimum accuracy, reliability and reproducibility. The use of extensometers and compressometers is encouraged to obtain precise measurements of actual specimen strain in fundamental units of inches per inch or millimeters per millimeter or percent. As a result of our uncompromisingly high standards of accuracy, you can have confidence in the data obtained from stress-strain diagrams produced with Tinius Olsen equipment. The figure below shows a typical diagram obtained from a metallic specimen. Notice the straight, clearly defined modulus line, key to accurate modulus and yield strength determinations.