Very interesting question--

[Ron Nossaman]

> I wonder what the limit is as to how far flat a piano will go if it is 
> never tuned. Let's say a piano was built in 1900, tuned many times in 
> the factory until the strings were stretched out and the tune stabilized.
> If it were never tuned after that, would it reach a point, let's say, in 
> the 1960's, 70's, or 80's where it would not go flat any more? And how 
> flat would it end up being -- 150 cents? 200 cents? I'm curious because 
> I've seen many old uprights that were about 150 cents flat, and I 
> wondered if they were /ever /tuned over their 100 year lifetime.
>  
> Jesse Gitnik

It's a diminishing rate of deterioration thing. The lower the 
pitch gets, the less tension there is on the strings and the 
less compression there is on the compressible parts who's 
further compression further lowers the string tension. So 
given a repeating seasonal profile over a number of years, a 
piano should drop less in the second ten years than it did in 
the first, and less again in the third than in the second, 
etc. I doubt that they ever quit dropping until they fall 
apart entirely.
Ron N