relative change formula seems wrong

[stvno]

While testing the application I noticed that lower average speeds have higher percentage changes when compared against the reference speeds. This is counter intuitive: a lower average speed should have a lower percentage change.
I checked the code and noticed that the formula to calculate the percentage change seems weird:

analyst-ui/src/app/processing.js

Line 33 in 0a9861d

geometry.percentDiff = ((refSpeed - geometry.speed) / mathjs.mean(refSpeed, geometry.speed)) * 100

The way I would assume would be (average-reference)/reference *100 as per https://en.wikipedia.org/wiki/Relative_change_and_difference
Any particular reason we are not using the simple formula?