Grist for the Mill

[Farrell]

I agree it would be interesting, but start with a decent STABLE AT PITCH 
(A440) piano - not a piano that you just did a 92-cent pitch raise on.

Terry Farrell

> 1992 01 pitch corrected 92 cents at A4 humidity 40% (including overpull)
> 1992 02 floated pitch at 7.5 cents sharp at A4 humidity 47%
>
> Today? Pitch correction at A4 of 31.6 cents and worst note of 120 cents
> humidity 29% (including over pull).
>
> Total pitch change over 160 months at A4 = 39.1 cents
>
> My "guestimate" is that for every 5% humidity change A4 drifts 4 cents.
> This would give around 14 cents of the pitch change for the humidity 
> portion.
>
> Plugging that value in makes the pitch correction at A4 more like 25 cents
> in a mere 160 months between tunings, or about 0.15 of one cent per month.
>
> I have no way to factor in humidity change for the worst note but if we
> ignore it then 120/160 =~ 0.75 cents per month.
>
> I hope more folks will do this sort of analysis and post it to the list--I
> found Conrad's data *most* interesting! Particularly that the piano was at
> 436.7 on 01/03 and a year later was 436.7 again. Too bad there was no
> measurement of room humidity to go with this!