This part of IEC TS 61244, which is a technical specification, reviews experimental techniques to quantitatively monitor the effects when oxygen is present during ageing of polymers in various environments including temperature, radiation or ultraviolet. Inhomogenous ageing effects caused by diffusion-limited oxidation are often encountered and provide theoretical equations to estimate their importance. These effects make it difficult to understand the ageing process and to extrapolate accelerated exposure to long-term conditions. It is widely known that mechanical properties degrade prior to electrical properties. These changes are consequences of chemical changes such as oxidation. In this technical specification, only mechanical or chemical monitoring techniques are of interest. This technical specification does not deal with electrical monitoring techniques.