try putting all Fs in the list. it will give the right answer the first time (1E) but instead of giving 1E for the rest, it adds one to the tens column each time it preforms another calculation. so the second time it adds F and F it will give 2E, the third time 3E, etc.
another thing: after three additions (about 180 ticks) the ones column stops changing this can be fixed with an erase and a furnace.
I did see also that 0+0=10 in your adder but I didn't see an easy fix. My browser is crashing because my parents are downloading something on the other computer so I'll look once I restart it.