A circuit that remembers what you told it. Welcome to sequential logic. Build an SR latch — the simplest one-bit memory cell.
Every gate you've built so far is combinational: outputs are a pure function of the current inputs. Flip a lever, the lamp reacts instantly. Flip the lever back, the lamp reverts.
A memory cell breaks that rule. Once you tell it "be on", it stays on even after you stop telling it. That requires state — the cell has to remember what it was last told.
The simplest memory cell is the SR latch:
That last rule — "do nothing, but keep the answer" — is what makes it a memory.
Place a Lever labeled Set, another labeled Reset, an SR flip-flop from the Flip-Flops palette, and a Lamp labeled Output. Wire:
The verifier will pulse Set, watch the lamp light up and stay lit, then pulse Reset, and watch the lamp turn off and stay off.
One-tick delay — flip-flops update on the next tick after their inputs change. That's why the "set pulse" rows show the output still at zero on the tick the lever first goes high — the new state is visible one tick later. Same model as a real digital flip-flop.
The SR latch has one notorious quirk: if you set Set and Reset both high at the same time, the output is undefined ("forbidden state"). In this engine we resolve it as "hold previous", but in real circuits that's a race condition you want to avoid. The next lesson — the D flip-flop — fixes this by gating writes behind a clock signal, which is how memory works in actual hardware.