With all the talk about exponential growth of the virus, logarithmic scales are popping up in graphs everywhere.

What is a logarithmic scale? Unlike those on a linear scale, the units on a logarithmic scale change. See the chart below.

The result is that the normally speaking rapidly growing line 10^x now appears as a simple straight line.

Exponential functions can be hard to graph, analyse and compare. Toning down the scale makes things more manageable. I remember in high school, I used log mm paper to plot graphs from physics or chemistry experiments. By measuring the incline of the line, I could estimate exponential coefficients, and compare them.

While logarithmic scales are a great practical tool for scientists, I think they are less useful in presentations to a more general audience. “Look at this straight line, but in order to understand how fast tings are really growing, look at the small numbers that reveal the axis measurements”. People simply don’t grasp the concept of a logarithmic scale. If the virus grows exponentially, well, show an exponential line.

If you need to compare exponential growth, make a bar chart of the growth rates, rather than drawing straight lines on logarithmic scales.