I need to define a best fit line for the linear portion of a set of data so that I can find where this line intersects with another line that I've already defined. This would be easy to do by plotting and using a trendline, however I would have to do this a few thousand times. If I can figure out a way for excel to at least define a range where the data is fairly linear, I can put a line through it. Any ideas? Maybe with a maximum standard deviation? I've attached a picture of a plot of data similar to what I'm using. The line with the negative slope is what I need to define.
Thanks!
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