VBA: Copy equation from graph to cell; update all if numbers in Y-coordinate changes

Hi, I am still looking for solution. Please, Thanks.

Does this all have to be done using the graph trendlines to get the equations, then VBA to copy the equations to a spreadsheet? My personal preference with this sort of thing is to use the LINEST() function to generate the equation coefficients directly in the spreadsheet. One LINEST() function for each data set will give you the best fit curve for each data set.

Is LINEST function for a straight line?

Yes, but it can do so much more than straight lines. The LINear in LINEST() is referring to linear equations as you would learn them in a linear algebra course (I'm sure a quick internet search should yield any number of tutorials introducing linear equations). For our purposes here, every one of the trendline options (except moving average) available in the chart trendlines is a linear function (or can be manipulated to be linear), so you can make a spreadsheet to make any of those functions using LINEST(). If you missed the help file, here's an online version http://office.microsoft.com/en-us/ex...010069838.aspx and it describes one way to use LINEST() to get polynomials in the paragraph just before example 1.

Please note the X and Y table will change dynamicly pending on another calulations

This is one reason I like to use LINEST() for regressions -- as the data updates, the spreadsheet calculates the new coefficients automatically.

Thanks for the help. I am going to try for myself first to learn and try and errors.
If I get lost and could not make it work, I may come back for help.

Best Regards,

=LINEST(C2:C20,B2:B20,5,4)

You are misunderstanding the arguments for the LINEST() function. The order of the polynomial is hidden in the known x argument. The 3rd and 4th arguments are booleans that simply tell LINEST whether you want to force the y intercept through 0 (3rd argument is FALSE, TRUE calculates constant term normally) and whether you want LINEST() to return the extra statistics (4th argument is TRUE to return values, FALSE to not return).

I found topics on LINEST, TREND, LOGEST, I am so confuse understanding. There are some examples in help, but I do not see any result with an equation, but a number.

Out of curiosity, how much of your confusion is related to the Excel specific functions, and how much of the confusion is related to understanding regression/curve fitting in general? I find the Excel functions are much easier to understand if I understand the math behind the function.

Here's a sample spreadsheet I created in Google docs (so I hope it converts back to Excel format). Note that I have created a column for each power of x that I want included in the known_x matrix (there are shortcuts for this when polynomials are involved, but this better illustrates exactly how LINEST() works with multiple x terms). I've used a 2nd order polynomial, it should be straightforward for you to add additional columns if desired.