'Tranfers Trendline text to cell as formula. The utility TrendlineToCell provided on the CD-ROM converts the Trendline equation to an Excel formula and transfers the formula to a selected cell on a worksheet. The disadvantage of Trendline is that the trendline equation is merely a caption in the chart to use it in the worksheet, the coefficients must be transferred manually by typing, or copying and pasting. Trendline provides a limited gallery of mathematical fitting functions, including regular polynomials up to order six. Its internal numerical algorithms can avoid or handle such errors.Scientists and engineers often use Excel's Trendline feature to obtain a least-squares fit to data in a chart. In contrast, the chart trendline algorithm works the original data. Part of the reason for that is: the input to LINEST is an array of values raised to powers up to 6 (in your case), which can encounter rounding error and computational limitations. LINEST sometimes returns an error or invalid coefficients (typically zero) when chart trendlines work properly. Apparently, there numerical methods for regression are not identical.Ģ. LINEST and chart trendlines do not always produce the same coefficients. That will ensure that you use values with 15 significant digits of precision, the best that Excel will format.Įven better: use LINEST (or LOGEST) to generate "the coefficients". But I think it is important to note the following.ĭo not use the coefficients constants as they appear by default in the trendline formula.Īny arithmetic based on those rounded values is likely to be off significantly.Īt a minimum, format the "trendline label" to display coefficients in Scientific format with 14 decimal places.
I do not have time to help you with the larger problem.
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