For example, with rubber, tear resistance measures how the test specimen resists the growth of any cuts when under tension, it is usually expressed in kN / m. Tear resistance can be gauged via the same ASTM D 412 apparatus used to measure tensile strength, modulus and elongation. ASTM D 624 can be applied to measure the resistance to the formation of a tear (tear initiation) and the resistance to the expansion of a tear (tear propagation). Regardless of which of these two is being measured, the sample is held between two holders and a uniform pulling force applied until the aforementioned deformation occurs. Tear resistance is then calculated by dividing the force applied by the thickness of the material.