What is Numeric "-/+" used for?

greets

I could not find an answer, neither in the AKAI manual nor on JJ's website. I thought that the -/+ could be used to increment digits, but it doesn't to do anything. Is it even functional in JJOS (since the MIDI to Button has the numerical -/+ option)?

I asked this not too long ago from JJ:

It is used for a parameter with the value of minus, such as TUNE.
After inputting a value, the -/+ key is pressed and the value of - or the value of + is determined.