post pitch-raise creep?

[David Nereson]

    I do many many many pitch raises -- almost every piano I
tune, for the last 27 years.  (Almost everybody lets them go too
long.)
    I've found that the ideal average overpull is halfway
between 1/3 to 1/2 the amount sharp as it was flat.  In other
words, a 41% overpull of the amount it was flat.  For an
easy-figuring example, say the piano is 18 cents flat.  Half of
that is 9 cents and a third of that is 6 cents.  Half-way
between 6 and 9 is 7.5, so I pull it 7.5 cents sharp, and almost
invariably A4 ends up right on 440 Hz, or very close.
    However, if the piano is a half-step flat, I don't pull it
41 cents sharp.  That would be too much.  There's some degree of
flatness where the usually-ideal 41% overpull has to taper off.
For a half-step pitch raise, I usually overpull so that A4 is
beating about 5 beats sharp.  That's approximately 20 cents, I
believe.  Sometimes more is required, sometimes less.  It
varies.  That's here in Denver -- probably different elsewhere.
    But what I often experience is:  even though after the pitch
raise, A4 is at 440; after I've gone through the fine tuning and
pulled in unisons, when I go back to do the final check and
touch up anything that has slipped, I find that the whole middle
section is sharp!  Why?
    --David Nereson, RPT


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