This is the part of calibration that separates the pros from the amateurs. Relying on visual brightness and contrast settings introduces too much variability into the system. For one thing, I think the Huey is assuming you'll have a really bad monitor (or really bad eyes); on the screen where it asks if I see three rings, I actually saw five, and there's no way to adjust the controls to see fewer. Setting the brightness and contrast values to 75% and 50%, respectively, is a suboptimal solution.
The directions can be a bit vague, as well. First you set contrast (the white/gray circle), then you set Brightness (the black/gray circle). But until you realize what each screen is for--they're not labeled as such--the instructions for Contrast are confusing. What does "it" refer to in the second sentence?