If you oscillate an air column, this causes nodes or nodal points at given positions. Naturally, these nodes have a significant influence on the tone and intonation of a wind instrument. If the inner diameter of the inner bore is altered, in other words, if you alter the thickness of the air column, these nodal points are displaced to another position. In the clarinet this displacement has a considerable effect on "overblowing" in the twelfth. Chalumeau improvement is thus nothing other than the art of modifying the inner bore to the correct positions, so that the intonation of the twelfth becomes either lower or higher. 
Specially developed tools, combined with delight in experimenting made it possible to design the inner bore to given nodal points in such a way that the limitations in intonation in our very wide Viennese bore can be reduced to a minimum. As the name implies, the intonation of the chalumeau register, G3 to D4 in particular has been improved by this innovation. This improvement also has a positive effect on the notes, C5 to E6.