(creator here) +1, the different digits add trivially as you say.

I also thought it was fun that when you overlay digits, you do get 1+4=5, 1+6=7, 1+8=9, 2+6=8, and 2+7=9 . That one I only found accidentally after a bit of playing, so the demo note is more of a fun side note than a really useful property.