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This part of ISO 148 covers the verification of the constructional elements of pendulum-type impact testing machines. It is applicable to machines with 2 mm or 8 mm strikers used for pendulum impact tests carried out, for instance, in accordance with ISO 148-1. It can analogously be applied to pendulum impact testing machines of various capacities and of different design. Impact machines used for industrial, general or research laboratory testing of metallic materials in accordance with this part of ISO 148 are referred to as industrial machines. Those with more stringent requirements are referred to as reference machines. Specifications for the verification of reference machines are found in ISO 148-3. This part of ISO 148 describes two methods of verification. a) The direct method, which is static in nature, involves measurement of the critical parts of the machine to ensure that it meets the requirements of this part of ISO 148. Instruments used for the verification and calibration are traceable to national standards. Direct methods are used when a machine is being installed or repaired, or if the indirect method gives a non-conforming result. b) The indirect method, which is dynamic in nature, uses reference test pieces to verify points on the measuring scale. A pendulum impact testing machine is not in compliance with this part of ISO 148 until it has been verified by both the direct and indirect methods and meets the requirements of Clauses 6 and 7. The requirements for the reference test pieces are found in ISO 148-3. This part of ISO 148 takes into account the total energy absorbed in fracturing the test piece using an indirect method. This total absorbed energy consists of - the energy needed to break the test piece itself, and - the internal energy losses of the pendulum impact testing machine performing the first half-cycle swing from the initial position.