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How wrong is your tracker? The ± on everything you measure at home
How wrong is your tracker? The ± on everything you measure at home: this guide has a section for each measurement, each giving the pooled error from…
This launch guide maps the topic, the source base and the practical questions. Check the linked official authority before acting on a rule, deadline, price or safety requirement.
What this guide covers
This guide has a section for each measurement, each giving the pooled error from published validation studies and ending with the honest sentence about what the device is good enough for: step count and where it over- and under-counts, distance and GPS drift, active calories (much the worst of the set), heart rate at rest and during intervals, HRV, pulse oximetry and the skin-tone problem, sleep duration and sleep stages against polysomnography, scale body-fat percentage, blood-pressure cuffs, home glucose meters against the ISO 15197 limit, thermometers by measurement site, and kitchen scales at small weights.
Fourteen pages, and it is the single most-asked question about every device in this category.
How to use it
Use How wrong is your tracker? The ± on everything you measure at home as a structured learning path: begin with the vocabulary, follow the evidence map, and keep the uncertainty labels attached to claims as you compare sources.
The page keeps the main question, its evidence base and its limits together in one canonical place. That makes it useful as a quick orientation and avoids splitting a broad subject into shallow pages before each narrower answer has enough verified material of its own.
Search vocabulary in four languages
Terminology changes across borders. These are example phrases people use for the same subject in Estonian, Finnish, Russian and English; they are included as a practical vocabulary aid, not as hidden keywords.
| Language | Example phrase |
|---|---|
| Estonian | kui täpne on nutikella sammulugeja |
| Finnish | onko älykellon kalorinkulutus tarkka |
| Russian | насколько точен фитнес-браслет |
| English | how accurate are fitness tracker calorie counts |
Evidence and provenance
The evidence map below records the primary, official or openly licensed material chosen for this guide. It is deliberately visible so a reader can tell the difference between a rule published by an authority, a measured dataset and an editorial explanation.
Source: published validation studies and systematic reviews (for example Fuller et al. 2020, JMIR, CC BY) plus the device standards ISO 15197 and ISO 80601-2-61, cited per page. · checked 2026-09-09
Source names are preserved even where an authority changes its web address. No figure is added to this launch page unless it is already present in the cited source description or can be computed from a named dataset.
Scope and boundaries
/gadgets judges whether a wellness product does anything at all; this is only about measurement error in devices people already own.
Connected TempoLife guides
The following paths are the intentional hand-offs named in the brief. They keep adjacent subjects separate while making the next useful reference easy to find.
Gadgets
Continue to the related TempoLife reference.
Bodycomp
Continue to the related TempoLife reference.
Vitals
Continue to the related TempoLife reference.
Why it belongs on TempoLife
/gadgets, /bodycomp, /vitals.
Frequently asked questions
What does this guide cover?
This guide has a section for each measurement, each giving the pooled error from published validation studies and ending with the honest sentence about what the device is good enough for: step count and where it over- and under-counts, distance and GPS drift, active calories (much the worst of the set), heart rate at rest and during intervals, HRV, pulse oximetry and the skin-tone problem, sleep duration and sleep stages against polysomnography, scale body-fat percentage, blood-pressure cuffs, home glucose meters…
What evidence does it use?
published validation studies and systematic reviews (for example Fuller et al. 2020, JMIR, CC BY) plus the device standards ISO 15197 and ISO 80601-2-61, cited per page.
Where does this guide stop?
/gadgets judges whether a wellness product does anything at all; this is only about measurement error in devices people already own.
Turn the reference into a routine
TempoLife brings food, movement, sleep and everyday health habits into one private place when you want to track what happens next.