iMPC pro tuning

Can someone pls explain this tuning option in the params mode to me?!
Its not like the semitone tuning on the other mpcs and sounds ... different

It aren't semitones since the app cannot determine which note the root note of the sample is (yet).

I guess it's in 127 MIDI "steps" (don't know how they're actually called) so you have to move the knob around and audition in comparison with a synth or other instrument to reach the note you want.