A trained eye can see 1/4 degree from 0. But it's not "at a glance" it's in operation. Such as watching wheel motion on specific roads/tracks.
Whether one can seen the difference between -2.4 degrees and -2.65 degrees is another story. I might have been able to discern a little more than this in years past, but not now. Mostly from years of tuning open wheel and conventional race cars.