Subtracting curves

[A.for.Andy]

Dear All

I am looking to subtract a baseline from graphs, but I have not found
a method of subtracting curves in Excel. More specifically, I am
looking to compensate for machine slack during compression testing,
thus the baseline will be consistent from data set to data set. A
colleague has designed a fairly complicated multi sheet workbook that
interpolates the data ranges before graphing, but it has it's errors
and is still not perfect. The best solution I have found so far is a
program called FindGraph, but I am hoping to find a solution within
Excel (ie: free!). Can anybody help?

Many thanks in advance

Andy

 

[Jon Peltier]

Are you offsetting all points of a series by the same amount? Then just add
or subtract the amount from each data value in the worksheet.

- Jon

 

[A.for.Andy]

Are you offsetting all points of a series by the same amount? Then just add
or subtract the amount from each data value in the worksheet.

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
Peltier Technical Services, Inc. -http://PeltierTech.com
_______









- Show quoted text -

Hi Jon

Unfortunately it's not as simple as that. While the data ranges
covered are the same, the data points within the ranges do not match
up across the ranges, hence the interpolation calculations being done
at the moment.

Andy

 

[Jon Peltier]

I missed the interpolation remark. You could either fit both series to a
curve (trendline) and use the fitting parameters to determine the
difference, or you could do the interpolation, wither using worksheet
formulas or VBA.

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
Peltier Technical Services, Inc. - http://PeltierTech.com
_______

Are you offsetting all points of a series by the same amount? Then just
add
or subtract the amount from each data value in the worksheet.

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
Peltier Technical Services, Inc. -http://PeltierTech.com
_______









- Show quoted text -

Hi Jon

Unfortunately it's not as simple as that. While the data ranges
covered are the same, the data points within the ranges do not match
up across the ranges, hence the interpolation calculations being done
at the moment.

Andy

 

[Del Cotter]

Unfortunately it's not as simple as that. While the data ranges
covered are the same, the data points within the ranges do not match
up across the ranges, hence the interpolation calculations being done
at the moment.

The important thing to realise is that this is not an Excel charting
question. Interpolation calculations are a matter of algebra. All Excel
Chart does is display points you give it via spreadsheet cells, and join
them up with lines. Any calculations you do would be the same whether
you were charting the result or not, so the posters here can't help you
except in so far as they may by chance know something about excel
functions. You're really better off asking in
microsoft.public.excel.worksheet.functions where the real function
experts are.

 

[PBezucha]

Dear Andy,
Don was absolutely right that the problem is in algebra. The second step,
however, is the necessity of using more complicated algorithm that is not
always free and at hand. What I would vividly agree with, is that VBA, as a
kind of second stage development in Excel, can largely facilitate the “smallâ€
work even in technical fields, provided the author is sufficiently familiar
in programming. No simple application of only worksheet functions would help
meaningful in this case, which should serve to routine (laboratory) work.
I happen to have done the same task as you, two months ago; the only
difference was that we perform flexural tests. The macro transfers a series
(force vs. time) from a measuring text file into a new Excel worksheet,
performs the conversion from time to deflection, and evaluates the slope
force-deflection (Young modulus) in the proper interval, etc. It really paid,
because the procedure is lucid, anomalies can be easily recovered and
treated, and numeric results be collected from individual lists to a summary.
Macro normally doesn’t require personnel educated in programming, as the
deployment is on a key combination.
The subtractive slack was here treated as a used defined function of a force
value, obtained really by an interpolation over a calibration series.
I would encourage you in offering some additional effort to remedy the
program of your forerunner that seems well grounded, only needs debugging.