Three weeks after Apple Watch Series 12 reached stores, the feature people are still unpacking is the readiness score, not the case colors. Official: the Health Sensing System samples heart rate more often — Apple highlighted a five-second cadence at the September 9 event — and turns that denser trace into a readiness number on Series 12. Aluminum starts at $399; Ultra 4 starts at $799. Both are already shipping. The open question is whether a faster pulse reading changes how people train, or just adds another number to ignore.