Excel - exponential x-axis in line/scatter charts

Factual Questions
1

I really thought this would be simpler when I charged down this road…

I’m trying to build a scatter chart in Excel that uses an N^1.85 x-axis. I’ve found an option for logarithmic scale (format axis/axis options), but that’s only letting me change the base to whole numbers, not decimals.

I have pondered adding a new column to my source data for labeling the x-axis, but that would require essentially rebuilding the whole spreadsheet, which I’d only like to do as a last resort.

How do I either fool the logarithmic scale into 1.85 or otherwise modify the chart to drag out the x-axis?

2

My SiL could actually answer this question but, knowing this place, you’ll have your answer before I leave work. If not, I’ll run it by her.

3

There was a Gnuplot Excel plugin; maybe that or some other plotting plugin might work?

4

Do you mean N1.85 or 1.85N? I’m assuming the latter.

All changing to a non-integer base will do is re-scale the vertical axis, since loga(x) = logb(x) / loga(x). In particular, the placement of the data points in the plot area will look pretty much the same, particularly if they take up the full range of the plot area. The only difference in the plots will be where Excel puts the tick marks along the horizontal axis; they’ll be at 1.850, 1.851, 1.852, 1.853 … The plot will look the same otherwise.

You may already know all of this, of course; I just figured I’d point it out so that you didn’t move heaven and earth to try to change something only to find that it make very little difference.

5

I did mean N^1.85. As the x-axis extends off to the right, the distance between points needs to increase. The intent is to take a curve that will always follow y=x^1.85 and make it a straight line as it plots out.

The graph is for showing how much water is available from a fire hydrant. Nearly all water flow graphs follow that N^1.85 curve. There’s even graph paper with the x-axis stretched for 1.85 that’s commercially available (has been for 70 years), I just want to do it in Excel. The current graph plots the curve, but I’m going for the traditional straight line if I can.

6

If you plot y = x1.85 as a log-log plot, don’t you see the straight line? Anyway, if Excel really won’t let you exactly replicate the special graph paper in a plot, then you can set up a plugin (example: xlwings + matplotlib) that will.

7

I concur with DPRK. Plotting a x^1.85 scale is non-standard and confusing. Far better to use a log scale for both axes, and either note that the slope of the line is 1.85, or else if you are plotting data points, include a separate reference line at y = x^ 1.85.

The only case where it would get you into trouble is if you have points around x=y=0

8

Well, we don’t know if it is non-standard and confusing— maybe there is a reason why the professionals need that particular graph (with the pressure drop on a linear scale).

Another option, if one is not allowed to change the spreadsheet, is to export the data, for example as CSV, and then you can handle the actual plotting in the external program directly, without having to deal with Excel plugins.

9

Could you try recasting your data so that a regular old linear plot gets you what you want? For example, if I wanted a logarithmic x axis I might make a column with log10(x) values and use a linear scale for the plot.