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Why matching trendline equation produces dissimilar curve on the same graph?

formamide

New Member
1. Sulfuric acid densities empirical table: column I concentrations in 0.5% increments, column II the corresponding measured densities.

2. I plot the curve "measured density"=f(%).

3. I plot the trendline as 5th order polynomial with R=1, perfect visual match.

4. Using this polynomial equation I calculate (in column 3) the new densities. This data is different from the measured densities.

5. I plot equation "calculated density"=f(%) on the same graph; the curve should match the first one, but it does not.

6. I plot the trendline for this second curve as 5th order polynomial; it is identical to the first equation.

The curves are clearly different, but the equations identical!! What am I missing here?
 
Formamide


Firstly, Welcome to the Chandoo.org Forums


Select the Trendlines Equation box and increase the number of decimals to 16

Try your equation again


Within Excel the equations are treated as Double Precision numbers, but by rounding the numbers in the equation box, they are truncated and missing obviously important data.


Refer: Limitations section in http://chandoo.org/wp/2011/01/27/trendlines-and-forecasting-in-excel-part-3/
 
Hui,

First of all, THANK YOU! It worked even with 6 decimals in scientific format.

Your succinct instructions directed me to "format trendline" rather than "format trendline label". However, after little fidgeting I got it right.

Problem Solved!
 
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