This International Standard describes three methods for the measurement of the change of stress in a test piece at a given elongation for the purpose of determining the ageing characteristics of a rubber. — Method A is intended for measurement under continuous strain conditions. — Method B is the preferred method for measurement under intermittent strain conditions. In the case of both methods A and B, a stress relaxometer is used to record the stress at the temperature of ageing. — Method C is an alternative to method B for measurement under intermittent strain conditions in which the test piece is removed from the ageing environment for measurement of the stress at standard laboratory temperature. The necessary calibration schedule for this type of measurement is given in Annex A. Measurements at a single elevated ageing temperature can be used for quality control purposes as a measure of heat-ageing resistance. Measurements at a number of temperatures can be used for research and development purposes to estimate long-term ageing characteristics in accordance with the procedures described in ISO 11346. No agreement between the three methods should be inferred. The method used will depend on the purpose of the test.