ISO 148-2:2016 covers the verification of pendulum-type impact testing machines, in terms of their constructional elements, their overall performance and the accuracy of the results they produce. 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 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.ISO 148-2:2016 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 or international standards.b) The indirect method, which is dynamic in nature, uses reference test pieces to verify points on the measuring scale for absorbed energy. The requirements for the reference test pieces are found in ISO 148-3.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 Clause 6 and Clause 7.ISO 148-2:2016 describes how to assess the different components of the total energy absorbed in fracturing a test piece. This total absorbed energy consists of- the energy needed to fracture 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.NOTE Internal energy losses are due to the following:- air resistance, friction of the bearings of the rotation axis and of the indicating pointer of the pendulum which can be determined by the direct method (see 6.4.5);- shock of the foundation, vibration of the frame and pendulum for which no suitable measuring methods and apparatus have been developed.