Why a personal baseline beats population averages
Wellness scores that compare you to everyone hide the early personal shifts that matter.
Last reviewed 2026-09-20 · Sources · Editorial policy
01The problem with normal ranges
Two healthy people can have very different usual HRV or RHR. Flagging someone for being outside a population band creates noise; missing a personal shift creates false calm.
02Median and MAD in plain language
The median is the middle night. MAD measures how spread out typical nights are. Robust z-scores ask: how unusual is today compared with your own day-to-day spread? Outliers move a mean; they barely move a median.
03Learning period
Until enough valid HRV and RHR nights exist, the app stays in Learning and withholds Off from usual alerts. Importing existing Apple Health history often unlocks a baseline on day one.
Guide FAQ
01How many nights do I need?
Sources
Public documentation cited as context—not as clinical validation of Early Signal.
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