First, most guitar tuners aren't sensitive enough to make 0.4 degree adjustments, and Second, there's no big sign that turns on and says "Ding, you've got it right

The needle in my chromatic tuner (a needle drawn on an LCD) wobbles a

If you need to do non-standard tuning, you'll have to use the strobe against a fretted string; for Drop D tuning, for example, you'll need to fret the low E at 2 and use E6 for comparison.