by pressing rec and minus you‘ll start subtractive recording mode.
i can‘t hear a difference…
anyone?
I took it to mean hold rec+minus to remove notes previously recorded, but I have not tried it yet.
what you mean is track and stop for clearing trigs
No- clearing notes: Section 3.6 of manual
subtractive recording
press ‘–’ while holding rec for subtractive recording mode. held notes will now be removed from active steps.
So the way I read it after you press - and record you then need to press the notes you want to delete.
i think it’s meant to be off grid recording without any stepping…like a time based track that would allow recording as long as you wish or reach the limit of 160 trigs per track.
it does have a reaction but it’s not recording anything ‚subtractive‘ the track keys just flash green for a sec
edit: they‘re flashing green by pressing record and - & red if you press +.
what is it
It is a special way to remove notes previously recorded. When you’re in the subtractive recording mode, any notes you press on the keyboard will be removed when the playhead hits a trig with that note on.
ah…like playing a Pad Sound between placed trigs but those laid trigs won‘t get overwritten while recording!? it’s a Dream Machine 
I
No its a realtime erase for the notes which you hold, say you have recorded a sequence of c,d,e,c,a on steps 1,3,5,9,13 now hold rec and minus and the c, and the c notes will be removed when the play led passes them. Or you could hold notes c and e and those would be removed when the play led passes, you can release the note buttons befor the end of the sequence or anywhere in between to only remove the notes that you held up to that point.
…but rec and shift is not rec and minus/plus!
Sorry that was a typo, I meant rec and minus. I corrected my post.
Rec and shift records any keys played as their step components onto track 13 in realtime, regardless of what track you are on it seems. You can quantize and mute it too and set the playback rate and length just as for any other track, pretty deep.
get the grip