Denner experimented with chalumeaux for a long time and finally managed to build an instrument that would not only play the lower register as well as the upper one, without losing too much intonation. The new instrument had such important changes it couldn't be called an evolution. He added two more holes close to the duodecimal key [ a system of counting or numerical notation that has 12 as a base ] with the help of his son. The addition of two keys might sound like a small improvement, but it made an enormous difference by increasing the musical range of the instrument by more than two octaves. Denner created a better mouthpiece so the player would have to correct the remaining problems with intonation with embouchure [the way a player puts their mouth on a mouthpiece of a wind or brass instrument]. Denner also improved the bell shape.