Just out of curiousity, why is this? I'm reading this page right here: http://newt.phys.unsw.edu.au/jw/fluteacoustics.html#registerhole A dark hole on the flute means the button is closed, and each white hole means the button is open (open to atmospheric pressure). You can see from the diagram that for every open hole, a node is formed in the corresponding wave. What about this exposure to atmospheric pressure makes this happen? Thanks.