Yeah, that was misleading.
For everything else with the +/- description I use my honeycomb bravo peripheral. Since it does not have a selection for the coms, I decided to use the c key on my keyboard, but still use a knob on this honeycomb peripheral to increase/decrease the value of com1.
That is why I connot guarantee that it works solely on keyboard, but in theory I don’t see why it would not work if you additionally assign keyboard keys to the “Plus” and “Minus” settings.
Hope I could clarify.