[pianotech] Pianotech: RE:Rib Scales Redux

[David Love]

Frank:

I see.  Actually you don't need to get that add-in function I don't think.
Once you run the trendline and get the formula you can just insert the
formula into a new cell and copy down using the rib numbers themselves as
the x values.  For example.  The following sequence of calculated values
from my string scale spread sheet transferred to the ribs (this is quickly
done and a bit rough) produced the following sequence of load numbers for
ribs 1 through 11:

17
63
78
43
57
70
69
88
87
92
57

That produced a trend line for a third order polynomial with the following
formula:

Y = -0.0742*x^3+0.4748*x^2+7.6836*x+27.085

So substituting the rib numbers for x it produced the following datapoints
for the trendline:

35
44
52
61
68
74
79
81
81
77
70

This matches exactly the original trendline.  While I was able to see the
formulas for the trendline I was never quite able to understand what to do
with it.  Now I know.  Thanks Frank and Steven.  I've copied this to the old
pianotech list as well just in case it gets lost in the new list shuffle.  

David Love
www.davidlovepianos.com


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David.
    At the following website you can download a user-defined add-in function
for Excel.  It's a free trial for 30 days and $30 to purchase.  You can set
up a table with the rib numbers in the X column and deflection data in the Y
column.    In a second table with the same X values, use the function to
return the smoothed values.  I didn't like the numbers for a second degree
polynomial, and used the third degree.  Of course you can enter different X
values that in the original chart, but that is not necessary in this case.
The add-in application is called Data Curve Fit Creator Add-in v2.2
    http://www.srs1software.com/

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George (Frank) Emerson, RPT
Silver Springs FL
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