# Exporting data from multiple data series' in a chart with consistent x-axis values

1. ## Exporting data from multiple data series' in a chart with consistent x-axis values

Hello there,

I'm sort of new here so please excuse my ignorance if I am asking a stupid question.

I have a simple chart that shows various data series' in parabola-type curves (positive and negative and a combination) rising (and falling, and in some cases, crossing) the x-axis.
I want to take one curve from another but the data that feeding the curves don't use the same x-values so I can't use the original data.
Is there a way I can take the y-values of the lines of a number of different data series' and export them so I can play with them?
Or is there a way that I can take one curve from another without doing this?

Thank you very much.

C

2. ## Re: Exporting data from multiple data series' in a chart with consistent x-axis values

Two possible approaches:

1) A curve fitting/regression approach. Regress an equation for each curve (use the LINEST function). Once you have the coefficients for suitable curves, then it is a simple matter to subtract one curve from the other.

2) A linear interpolation approach. Assume each data point is connected by a straight line. Calculate both y's at a given x, then subtract. The hardest part of linear interpolation is looking up and returning the endpoints of the interval that contains the desired x. Once you have that, the interpolation formula is simple (y2-y1)/(x2-x1)=(y3-y1)/(x3-x1). If you are allowed a different spreadsheet some other spreadsheets (such as QuattroPro) have built in linear interpolation functions that make this easy. Excel doesn't have a built in function so Excel users have to build the interpolation from the MATCH and INDEX functions.

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