This part of IEC 60076 provides supporting information to help both manufacturers and purchasers apply the measurement techniques described in IEC 60076-10. The sources and characteristics of transformer and reactor sound are described. Practical guidance on making measurements is given, and factors that may influence the accuracy of the methods are discussed. This application guide also clarifies those factors which should be agreed between manufacturer and purchaser when specifying a transformer or reactor, and indicates why values measured in the factory may differ from those measured on site.This application guide is applicable to transformers and reactors together with their associated cooling auxiliaries.