On my Elkhart 300 culy sop the body octave key has 2 pads.The one that covers the tone hole has hole through the middle and another pad covers this. When the octave key is pressed the lower pad lifts the upper until reaches c# when the lower closes but leaves the upper open. This then stays open all the way to top F#. This does not exist on any of my other saxes. What is it for? The key is the one immediately under the front Ftouch.