A compression test determines behavior of materials under crushing loads. The specimen is compressed and deformation at various loads is recorded. Compressive stress and strain are calculated and plotted as a stress-strain diagram which is used to determine elastic limit, proportional limit, yield point, yield strength and, for some materials, compressive strength.   It is used to measure the compressibility of a material as well as the recovery of a material that has been compressed to a load and held over a time period.  The maximum stress a material can sustain over a period of time under load (constant or progressive) is determined. This testing is typically used to test plastics, foam, rock, concrete and asphalt. It is rarely used to test metals. It is also used in product testing to evaluate the behavior of finished products. For example, a hypodermic needle may be pushed into a material to see how easily it penetrates and to assess its sharpness.