Comments on: Logarithmic Axis Scales

By: Rob Beal

Rob Beal — Wed, 30 Mar 2011 20:48:08 +0000

Jon-
Great work and great website, your techniques are very helpful in working within the limitations of excel. Log plotting is a technique that I prefer to use for many data series, but I only do it occasionally because of the extra work at building the charts in excel. Do you know if Microsoft improved log plotting in Office 2010?
Thanks!

By: Mario Marinato

Mario Marinato — Mon, 23 Mar 2009 12:34:18 +0000

Jon,

Thank you very much for you posting. I’m working on a open source software that plots financial graphs but it had a broken log-scale-plotting-function which I had to fix. After a few days of some misleading readings I discovered your explanation and it gave me the clues I needed to solve the problem.

Your writing is really clear. Congrats!

Again, thank you very much.

Mario Marinato, from Brazil

By: Jon Peltier

Jon Peltier — Sat, 20 Dec 2008 13:44:38 +0000

Siren -

The nature of logarithms is that you can only convert positive numbers to logs, with the resulting logs covering the range of ± infinity.

You can always fake it. I have a number of samples on my main site that show various Custom Axis Scales using Dummy Series. Most involve adding a helper (or “dummy”) XY series to create the axis, then transforming the data to accommodate this dummy scale

You would have to decide where your line of symmetry would be. For example, you could have the positive values go 1, 10, 100, etc, and the negatives go -1, -10, -100, etc, with +1 and -1 occurring at the same point. To get your negative values to plot, you need to transform them using something like -log(-value).

Alternatively, you could select a ± range that will be linear in the middle, with log values extending outward from this range. So the scale would go
-100, -10, -1, 0 ,1 , 10, 100, etc., with the data plotted linearly between -1 and +1.

By: Siren

Siren — Sat, 20 Dec 2008 05:48:14 +0000

I’ve been trying for some time now to find a way to use a log-like axis scale that includes negative values.

Basically what I’m looking for is:

Tick marks, each an inch apart, on the positive Y axis, labeled: 10, 100, 1000, 10000, …
Tick marks, each an inch apart, on the negative Y axis, labeled: -10, -100, -1000, -10000, …

It just seems wrong that I’m allowed to scale positive values but not negative ones. Can you help? :)

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