Chapters: Overtones and intervals. Types of octaves & double octaves. Aucral checks and setting instructions. Compromises between various types of octaves and double octaves. Why different types of octaves are tuned in particular areas of the piano. How varying the level of partial matching causes varying degrees of out-of-tuneness. Executing compromises in areas of transition. Compromises in the bass. Other interval tests. Theoretical basis for octave and double octave tests. Conclusion. Appendix.