German clarinets and a growing number of Boehm system clarinets, especially high end clarinets, have a pad on the lower joint between the and pads. This pad cannot be operated independently, as it closes with activation of the pinky fingers controlling (or )
I assume this aids in tuning. My question is what is the theory behind this pad, and why is it only fairly recently appearing on contemporary clarinets? Is it worth the extra weight, need for adjustment, and whatever increased cost it entails?