"Why a string goes out of tune"

[James Ellis]

I tried to answer Wim's original question by saying there are many reasons
why a single string goes out of tune.  Just look at the piano, and
visualize all those metal-to-wood interfaces, wood grain running in
different directions, no two strings that are identical, etc.  There are
microscopic movements going on all over the place all the time due to
temperature and humidity changes.  The amazing thing to me is the fact that
the piano is as stable as it is, while sitting there with all that tension
of the combined strings pulling on it all the time.  I tried to answer what
I thought to be an honest question with an honest answer, and I am in no
mood to argue about it now.  With that comment, I take the exit on this
particular subject.

Sincerely, Jim Ellis