The hardness (H0) of the test piece before it examines it is measured by the measuring method of 3.3. Place the test piece on the platen perforated with small holes,and carry out pounding for continuous 80000 cycles to 50% of the ghickness of the test piece at a speed of 60 cycles per min. Thereafter, take out the test piece, let it stand for 30 min under conditioning environment specified in 3.c), and remeasure the hardness (H1) by the same method of 3.3. Three kinds of hardness goods are measured respectively once.