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GET the EQN from trendlines.... and more

  1. #1
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    GET the EQN from trendlines.... and more

    I am plotting gas ppm response x,y curves and adding trendlines to fit. I want to access the EQUATIONS on my sheet. I could copy and paste a, b, and c for 100 diferent lines but I would prefer it be done a little faster than that. I know VBA - maybe that could select the best trendline match, given lin, exp, polynomial....

    My chart experiance SUCKs.... just saying...


    Here is sample of data:
    Name ppm Rs/Ro
    Smoke 200 3.9
    1000 3.65
    10000 2.5
    CO 200 4
    1000 3
    10000 1.5
    Met 200 3
    2000 1.5
    10000 6
    R-OH 200 3
    2000 1.5
    10000 6
    H2 200 2
    1000 1
    10000 0.22
    pro 1000 0.8
    200 1.7
    10000 0.27

    I want to get a ppm from a given Rs/Ro ratio - figure eqn is the answer... so how do I automate this?!

  2. #2
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    Re: GET the EQN from trendlines.... and more

    Are you required to use the chart trendlines for this, because I would do all of this in the spreadsheet (except for the visualization). All of the available trendlines in the chart are linear (or can be made linear), so I would use the LINEST() function to get parameters for each trendline that I wanted to try (https://support.office.com/en-us/art...a-fa7abf772b6d ), measure "best fit" (not sure how you want to measure goodness of fit), then choose the desired trendline from that.

    I'm not sure of all your requirements for this, but I would try to do most or all of the work in the spreadsheet. The chart would be useful for visualization of the result, if you want to visualize it at the end.
    Quote Originally Posted by shg
    Mathematics is the native language of the natural world. Just trying to become literate.

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