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Best Fit??

S

Shoebird

Member
Is there a function that I could use on three data points that would provide the best fit funtion for three data points.

I have about 70 fans that I would like to use the affinity laws to predict the power consumption based upon speed. The kicker for me is due to the dynamics of the installations, there is a loose relationship between theory and application. It would be best to use a best fit equation for each application similar to a 2 order polynomial. Any help would be appreciated. Thank you and happy holidays to all!
 
=LINEST() will generate a linear best fit
=LOGEST() will do a log fit

That's about as fancy as Excel's built-ins go. There are several add-ins that would probably do a better job.
 
Shoebird said:
As always Hui, great answer. Still having some problems but I will spend some time working through the links and see if I can resolve the problem. The main problem that I am having is major issues between calculated values and real world values.
Click to expand...
Okay, still have issues with the equation. Here is what I have:
X data points are:60, 80, 100
Y data points are: 1.55, 3.49, 4.79
When I do the trendline for the graph, I am selecting a 2nd degree polynomial, display equation on chart, and display 4-squared value on chart. My equation for the line is -0.32x^2+2.9x-1.03 with an R^2=1.00.

When I plug in 60 for my x (-0.32*(60)^2+2.9*(60)-1.03) will result in -979.03. Not 60. Thoughts?
 
I would also select the Formula Box where the Formula is and increase the decimal places to say 6 or 7
Then use those factors in your formula
 
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