What exactly does it mean to meet the requirements for springs regarding an inspection every 3 years for safety valves?

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The \"TSG 21-2016 Safety Technical Inspection Regulations for Fixed Pressure Vessels\" states that one of the conditions under which a safety valve can be inspected every 3 years is that the manufacturer of the safety valve must be able to provide proof that the springs used have been subjected to stress treatment or heat-treated stress treatment in accordance with GB/T12243 \"Spring-loaded Safety Valves\". Additionally, 10% of the springs of the same specification from the same heat treatment furnace (but not less than 2 springs) must be tested for their deformation under the specified load or their stiffness, with the deviation in the test results not exceeding 15%. What exactly are the numerator and denominator in this 15% figure? For example, if the original length of spring A is A_original, then its length after compression is A_compressed； The original length of spring B is B_original, and its length after compression is B_compressed. As I understand it, there are two interpretations for meeting the conditions: one is, (A_original – A_pressure)/A_original