Apple's system-in-package for the Apple Watch, carrying the watch's main processor and on-device machine learning silicon.
MacRumors' buyer's guide puts the Series 12 and the Ultra 4 on the same S11 chip and the same Health Sensing System, so the $400 between them, and the $500 inside the Series 12 line, buys endurance and case material.
Reality
Apple's evidence for calling the Ultra 4's new optical sensor the most accurate in a wearable is a white paper Apple published, drawn from a study where most participants wore competitor watches on the other wrist. DC Rainmaker is testing it outdoors.
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Siri Recap summarises a wearer's conversations, and there is no audio file at the end of it. The attorneys Bloomberg asked about it say a state eavesdropping charge would reach the wearer.
Reality
Apple has stopped selling the Series 11 at the same moment Readiness, Recovery HRV and Audio Intelligence became exclusive to the Series 12, so any mixed deployment now supports two different feature sets.
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Apple built the wearer a careful consent flow for the Watch's new listening features and built nothing for the person across the table. That is the part it will have to answer for when it moves to glasses.
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Apple left the Ultra's case, display and price where they were and spent this year's upgrade underneath, on the sensor array and the silicon. What the watch can measure now depends on hardware a software update cannot supply.
Reality
The Series 12 samples heart rate every five seconds and HRV far more often, but the features Apple leads with are judgments built on that data: a readiness score, and a Health Age that grades you against your own age.
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