Need to make a graph with 1 y-axis and 1 x-axis - but from multiple datasets

Here's what I did (starting from the first file in post #1):

1) Select the first x,y columns (A and B) and insert a scatter chart (straight lines without markers).
2) Bring up the Select Data dialog, add a new data series, and tell it to use C and D for the X values and Values respectively.
3) Repeat step 2 until all data series have been added to the chart.
4) Format chart elements as desired.

It should be as simple (if a bit tedious) as that. Does that help?

I'm optimistic enough to believe that spreadsheets can be programmed to perform most data analysis tasks (even if a spreadsheet isn't the best programming language for the task). I doubt there is a "perform the desired analysis at the click of a single button" tool preprogrammed into Excel for this, but, if you understand the desired analysis well enough and are willing to program the individual steps needed, a spreadsheet can do many different kinds of analyses. For example, if I decide that I want to see what an exponential decay model does for this data, I would:

1) First step for most of the analyses that come to my mind for this will be to make a copy of the data with all of the values in a single table (all of the x values in one column and all of the y values in 1 column). If you have access to it, the VSTACK() function can readily perform this task (https://support.microsoft.com/en-us/...a-fcc10d795a9c ). Power Query can also do it. Or you can do as I did and just manually cut/copy and paste the separate data sets into one combined data set.
2) Some analyses (like a moving average) might require you to sort the data by x value. If your analysis requires you to sort the data, Excel has a sort command. If you have access to it, there is also the SORT() function https://support.microsoft.com/en-us/...d-c20e8e44b86c . Power Query can also sort data.
3) I can compute the parameters for a basic exponential decay function using the LOGEST() function https://support.microsoft.com/en-us/...rs=en-us&ad=us

With appropriate intermediate steps, I can expand on this to perform a variety of other "linear" regressions (like a polynomial trendline) using the more generic LINEST() function. If I am trying a moving average function, the AVERAGE() or AVERAGEIFS() functions would be useful here. Excel has a built in exponential triple smoothing algorithm programmed as part of the FORECAST.ETS() function.

4) From the regression constants, I can add a column to calculate the estimates from the regression equation in an adjacent column and perform some "goodness of fit" calculations and do other things to evaluate the results of the analysis. After calculated the regression values, I can add those values to the chart as a visual way to see how the regression did and that may help in evaluation.

Spreadsheets are a powerful programming language for performing data analysis, but, like other programming languages, spreadsheets cannot do everything at the click of a single button. When you understand the analysis you want to perform and the tools that a spreadsheet provides, you can program a spreadsheet to do a variety of analyses.