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#1




Excel graphing and equation issues
Okay so here is my problem. For work, I have a curve that I need to put into
excel and find the equation. So I look at the curve and record data points from the curve into excel. I will then graph the points and it will produce a curve just like the one have on paper. My problem comes when I ask excel to produce equations for the curves. The equations it produces do not match the curves when I enter a value into the equation. Why does this happen or how can I fix it? 
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#2




Excel graphing and equation issues
Make sure you start with an XY chart, not a line chart. Then make sure
the equation has enough digits, so apply a scientific number format with 15 decimal places.  Jon  Jon Peltier Peltier Technical Services, Inc. http://peltiertech.com/ On 4/29/2010 4:23 PM, danklebs wrote: Okay so here is my problem. For work, I have a curve that I need to put into excel and find the equation. So I look at the curve and record data points from the curve into excel. I will then graph the points and it will produce a curve just like the one have on paper. My problem comes when I ask excel to produce equations for the curves. The equations it produces do not match the curves when I enter a value into the equation. Why does this happen or how can I fix it? 
#3




Excel graphing and equation issues
Better let’s repeat your procedure. You read out several coordinate pairs on
a curve from some graph. You transferred them into an Excel spreadsheet. You created a xychart. In it, you created a regression line (“trend line”), for example a quadratic one: y = a0 +a1*x + a2*x2. You read the regression coefficients a0, a1,… from the text box pertinent to the series of your points. You tried to write the formula in Excel having the same form as the regression function. You found out that the results after substituting x’s do not give the expected results. Most probably you are making some basic mistake (wrong constitution of the equation,+/, wrong transferred coefficients etc.). First after eliminating such trivialities you can test the influence of insufficient accuracy. More transparent method is a direct statistical treatment of data (LinRegression and similar functions).  Petr Bezucha "Jon Peltier" wrote: Make sure you start with an XY chart, not a line chart. Then make sure the equation has enough digits, so apply a scientific number format with 15 decimal places.  Jon  Jon Peltier Peltier Technical Services, Inc. http://peltiertech.com/ On 4/29/2010 4:23 PM, danklebs wrote: Okay so here is my problem. For work, I have a curve that I need to put into excel and find the equation. So I look at the curve and record data points from the curve into excel. I will then graph the points and it will produce a curve just like the one have on paper. My problem comes when I ask excel to produce equations for the curves. The equations it produces do not match the curves when I enter a value into the equation. Why does this happen or how can I fix it? . 
#4




Excel graphing and equation issues
Rather than copying the trendline parameters, use LINEST to place their
values in worksheet cells. This gives you full precision and the values get updated should you correct the charting data. For more see http://people.stfx.ca/bliengme/ExcelTips/Polynomial.htm http://people.stfx.ca/bliengme/Excel...&%20LOGEST.htm best wishes  Bernard Liengme Microsoft Excel MVP http://people.stfx.ca/bliengme "danklebs" wrote in message ... Okay so here is my problem. For work, I have a curve that I need to put into excel and find the equation. So I look at the curve and record data points from the curve into excel. I will then graph the points and it will produce a curve just like the one have on paper. My problem comes when I ask excel to produce equations for the curves. The equations it produces do not match the curves when I enter a value into the equation. Why does this happen or how can I fix it? 
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