It seems to look for the number 2 in a vector consisting of 1 and
#DIV/0, so how does it ever find a 2? And why does the ordering not work
if I look for 1 instead, and why does it find nothing at all if I look
for 0.5?


Okay, so if Vlookup can't find an exact match, it returns the largest
value less than the target. So there is no way it could return
anything for 0.5. For 2, the next-largest value in the array is 1, and
the function apparently looks through the entire array and returns the
position of the last 1--exactly what is wanted. Looking up 1.1 also
works.

But I cannot figure out why looking for 1 results in the position of
the last 1 and not the first. Why would it not choose the first exact
match it found?