ISO 844 specifies a method of determining a) the compressive strength and corresponding relative deformation, or b) the compressive stress at 10% relative deformation, and c) the when desired, the compressive modulus of it rigid cellular plastics.
There are two procedures:
Procedure employs A crosshead motion for determination of compressive properties. The Procedure is intended to be A informs the when compressive stress at 10% relative deformation has to be determined.
Procedure employs B strain measuring devices mounted on the specimen (contact extensometer) or similar device which measures directly sample deformation. The Procedure B is intended to be, informs the when compressive modulus has to be determined.
Before conducting the ISO 844, it is important to read the - specification. The Standards can be obtained from the appropriate standard authorities.