The setup slider seems to respond only in full-integer steps.  For instance, there's no difference between -10.3 and -10.4.  Is there a way of accessing values between the full integers?  The scale shows these values, but they have no effect on the image.

MC 19.12.0/ Mac OS 10.14.6

MC 6.5.4/ Mac OS 10.8.5

How do you have your Video Quality set? In Yellow/Green (draft mode) or Green (8-bit full mode) you'll only see integer adjustments, but in 10-bit Green or 32-bit float Blue you'll see finer adjustments work.

Thank you so much for this.  I never would have figured it out on my own.  I assume that changing the Video Quality to 10-bit green affects only the display on the monitor: in other words, at the plain green setting, Media Composer changes the parameters of the image on the file but they're not visible on the display.  In any case, it works now.  Again, Many thanks.

Yup, that's basically right. I believe the Colour Corrector always works internally at 12-bit res, but what you see is down-converted to whatever bit depth you have selected on the Video Quality button.