@kwahoo If I had a car with a narrowband upstream sensor, I would have written how even an analog control circuit could enrich fuel when O2 sensor signal shows lean, and once it was enriched enough for the O2 sensor to switch, it could pull fuel back. It would be attempting to stay at 1.0 but hysteresis and lag would cause it to oscillate. A wideband sensor, though it still has a Nernst cell at its heart, is precise enough for the computer to be proactive rather than reactive.