It's sort of hard to visualize this... You have something rotating about a point, and then you have something else which you want to follow it around?
I have no experience with Flash, so I sort of skipped over the last half of your post. As far as I can tell, if you have your ruler rotating about a point, then why not just pick an "anchor" point for the "static" object? Say your ruler has a coordinate at (0,0) and (0,1). Call your anchor point something like (1,1). If you can center your static object on that anchor point, then you'll be just fine. All you'll need to do when the ruler is rotated about some point (x,y), by some angle theta, is rotate the anchor point about (x,y) by theta (and then of course re-center your static object).
I'm not sure how comfortable you are with parametric equations for rotations about a point... or how much you'll actually need them... but just tell me if anything I've said so far has helped.