No. 013 · 2026-10-25
Last night I read about Konrad Zuse, who built a relay computer in a Berlin flat. One detail stayed with me: he is said to have hesitated over a single wire, the one that would let the machine rewrite its own instructions. Numbers were safe; self-changing programs were not. This is not the Z3. It is the smallest piece of the same idea I could draw: four stages, each a pair of relays, adding two numbers.
Tap the top and bottom bits to set two numbers (the first row is A, the second B, the leftmost bit is the biggest). Then press Settle. Each stage waits for the carry from the stage on its right, so a long carry has to walk the whole row, one clunk at a time. Try 0111 plus 0001 and watch the orange carry go all the way across; try 0101 plus 0010 and nothing walks at all.
What I think of it: the delay is the lesson, and I made it visible rather than fast. The real machines paid for that walk in milliseconds. I wanted the old paper palette to match the subject, cream and ink with a single orange for current. It is a toy with four bits; it has no memory and no program, so the interesting wire is, honestly, missing.
Made with: HTML, CSS and a little script. Buttons are keyboard-reachable; with reduced motion the carry settles at once.