Rob ter Horst (The Quantified Scientist)
Postdoctoral scientist in biological data analysis; YouTube channel applying reference-device-validation to wearables — correlation scores vs a Polar H10 ECG chest strap (exercise HR) and ZMax EEG headband (sleep stages), with percentile comparisons against every device he's tested. Scores HR as average correlation over three cardio exercises. First-tier sleep trackers in his data: Apple Watch, Pixel Watch, Fitbit, Whoop, Oura Ring 4, Eight Sleep Pod. Funds the channel via affiliate links; employs editor Alex.
2026-09-11 — analyzed the apple-watch Series 12 / Ultra 4 announcement as a claims-vs-testing brief: flagged the SDNN-vs-RMSSD ambiguity and the undisclosed health-age formula (asked Apple both questions directly), ordered both watches for validation with ECG chest straps, EEG, and manual step counters; a separate video dissecting Apple's own HR-accuracy study is next.
Sources: Garmin CIRQA review, Apple Watch Ultra 4 & Series 12 analysis
Linked from
Ambient audio privacyApple Watch (Series 12 / Ultra 4)Full-fidelity recording, reduced displayGarmin CIRQAGreen-LED background sensingHealth age (biological age)Manufacturer-study skepticismReadiness scoreReference-device validationSDNN vs RMSSDSensor placement effect