The SR22 has built-in oxygen, the SR20 does not, but it does have any empty plate for where the oxygen button would go. Does anyone know or have a diagram of what's involved behind-the-panel for the Cirrus's built-in oxygen system? Is the panel mount switch also the regulator and it simply connects up to the oxygen bottle so all you need is the panel switch plus oxygen bottle? Also, where is the oxygen bottle mounted? Bonus question: what goes in the empty slot between the oxygen switch and the flaps switch? It looks like it's designed for something to go there but I've never seen anything in that spot on any Cirrus's.