I can see that I didn't account for the case where we were on the line of due north, but surely the example wasn't a complete loss?

You can easily check to see if x1=x2 and if so, compare the
y values. If x1=x2 then the angle will be either 0 or 180,
so you have to hard code this test.

I was of the assumption that the problem you were having
was in all the other possible places to click. You
wouldn't have needed anyones help to figure out that if you
click directly below, it is 180 deg, and directly above is
0 deg?

Examples posted here are meant to get you started on your
own discovery of a solution. I for one never assume I can
provide code that is 100% guaranteed to fit your project

I believe the math in my example should get you going..If
not, well then I guess it is beyond us both huh ?

hehe