MEASURING, TESTING AND X-RAY MACHINES AND INSTRUMENTS, NAMELY, ELECTRONIC APPARATUS FOR MEASURING AND TESTING STRESS, STRAIN, HARDNESS, EXTERNAL FORM AND SURFACE ROUGHNESS FOR USE IN NON-DESTRUCTIVE INSPECTIONS OF THE SURFACES AND INSIDES OF INDUSTRIAL MATERIALS, PRODUCTS AND COMPONENT PARTS AND OF SHOT-PEENING-TREATED INDUSTRIAL MATERIALS, PRODUCTS AND COMPONENT PARTS; AND X-RAY STRESS MEASURING DEVICE