The add button doesn't work unless you spark the PSCN... it can get annoying...
Funny, I made the same kind of mech a while ago (I think, I haven't opened yours yet).
I like it. Can you explain it more thouroughly for us mniip?
I made this a year or two ago. Has been the most effective way for easily performing addition that I have found.
https://powdertoy.co.uk/Browse/View.html?ID=518889