This part of IEC 61400 deals with mechanical load measurements on wind turbines. It mainly focuses on large (>40m 2) electricity generating horizontal axis wind turbines. However, the methods described might be applicable to other wind turbines as well (for example, mechanical water pumpers, vertical axis turbines). The object of this specification is to describe the methodology and corresponding techniques for the experimental determination of the mechanical loading on wind turbines. This technical specification is intended to act as a guide for carrying out measurements used for verification of codes and/or for direct determination of the structural loadi