Fredxx wrote:
Just keep an eye out for any changes.

There might be something you can do in terms of fixing some cheap laser
pointers (firmly) to the structure, and marking out where the beams land.
Then go at different times of day and see if there's any difference.
(turning them off when not in use, obviously!)

(I'm not sure laser pointers are collimated enough, but worth a try before
going for anything fancier)

Theo