First, place $A L B E D O$. We then note that $I C A O$ has two orientations, both of which have $I$ on $E O$. Next, we note that for any given orientation of $I C A O$, the two orientations of $V E N T I$ have $N$ symmetric to line $E I$. Thus, for any given orientation of $I C A O$, we have that $O N$ is the same in both orientations of $V E N T I$, which gives a total of 2 possible values for $O N$.