Aha! was flat facts

[Ron Nossaman]

> And herein lies the interesting crux of my whole question from the
> beginning: We have guesses, suppositions, and opinions but, apparently,
> really don't know why pianos get flatter and flatter and flatter over time.
> Seems like this question is so basic that experiments would have been done
> long ago and we'd have a definitive answer. And maybe, who knows, some ideas
> for building more stable pianos.

There have been experiments, including making pins so tight in 
waterproof pinblocks that you could barely turn the pin in with 
three hands. Guess what. The super tight waterproof block pianos 
still dropped in pitch over the long run. In my experience, tuning 
stability gets better with decent scaling, rib supported boards, and 
laminated bridge caps. Hence my answer.

> I still go with turning pins, though. There is a natural, sustained tension
> on the pin from the string that would love to turn the thing
> counter-clockwise. Earth tremors, children thudding across the floor, sonic
> booms, moving the piano, and hovering ufo's would all put vibration into the
> system, however briefly, and the pin could jiggle just a a third of a skinny
> hair each time. But over the years ...

Is that a guess, a supposition, or an opinion? Just asking, since 
the same rules ought to apply to us all.
Ron N