I suspect it was designed to work on analysing a 'standard' negative.
The content of the negative I don't know anything about.
Some analysers integrate by way of diffusion to arrive at a neutral grey.
Others may follow a more of a process strip approach ie perhaps a dark spot to judge developer (or more specifically, exhausted bleach) activity by, a light spot to look for staining, and a grey spot to check for the right dilution/time/temperature/replenishment rate of the developer, and perhaps to also judge the exposure filtration and lamp intensity/aperture/time settings.
A picture, or at least naming the knobs, and the increments they are divided by may help my general explaniations become more specific.
And, yes, Colour printing means training your eye, despite what all sorts of toys are there to help.