This part of ISO 4263 specifies a method for the determination of the ageing behaviour of rust- and oxidation- inhibited oils having a density less than of water, used as turbine oils (categories TSA, TGA, TSE, TGE of ISO 6743-5, see [4] in the Bibliography), hydraulic oils (categories HL, HM, HR, HV, HG of ISO 6743-4 see [3] in the bibliography), and circulating oils (category CKB of ISO 6743-6 [5] in the bibliography). Oils containing synthetic components can be tested by this procedure, but no precision statement is available yet for such fluids. NOTE 1 For the purposes of this part of ISO 4263, the term "% (m/m)" is used to represent the mass fraction of a material. NOTE 2 Other signs of oil deterioration, such as the formation of insoluble sludge, catalyst coil corrosion or decrease in pH value, may occur, which indicate oxidation of the oil, but are not reflcted in the calculated oxidation lifetime. The correlation of these occurrences with field service is under investigation.This test method is widely used in specifications and considered of value in comparing the oxidation stability of oils that prone to contamination with water. However, because of the large number of individual field-service applications, the correlation between the results of this test and actual service performance can vary markedly, and is best judged on experience. The precision of this part of ISO 4263 for oxidation life was only determined on inhibited turbine oils, and applies to oxidation lives of 700 h to 3900 h.