A universal testing machine is used to measure the mechanical properties of materials in tension, compression, bending or torsion.  Mechanical properties of interest for plastics in bending are Flexural Strength, Flexural Stress at Break, Tangent, Secant and Chord Modulus of Elasticity.  ASTM D790 Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials governs the flexural testing of plastics.  In bending, a testing machine is used to create a stress-strain diagram (Figure 1) from which all mechanical properties are derived.  A true picture of the stress-strain diagram can only be obtained through accurate measurements.