It use fftw3 and tracking maxima.
In the tuning range it is good for ~ 0.02 Cent
Can't answer that for the MOD, maybe falkTX can.
I guess that the complete range of the display is +-49 Cent.
In my stand alone implementation, I have split the range of the bars, so that the last 10 Cent before match, get a wider range then the remaining 39 Cent.
That is visible by marks in the display.