The Physiology Behind the Numbers
Plain-language, clinically framed explainers on what our apps measure — grounded in the literature, honest about what's established versus still debated.
PPG Basics: How Your Phone Reads a Pulse
What photoplethysmography measures, how a fingertip camera scan turns light into a heartbeat, and where phone-based PPG's real limits are.
Read article →Heart Rate Variability, Explained
RMSSD vs. SDNN vs. LF/HF — what each metric is sensitive to, and why "normal" HRV doesn't exist as a single number.
Coming soonThe Pupillary Light Reflex as an Autonomic Window
Why the pupil's reaction to light is a genuine autonomic signal, and how camera-based measurement compares to clinical pupillometry.
Coming soonCamera-Based Movement Tracking, Explained
What phone-camera motion analysis can and can't tell you about joint range, gait, and movement quality.
Coming soonHow we decide what's sensible to claim
- We cite the primary literature, not secondary summaries or marketing claims, and we name the source so you can check it yourself.
- We separate established science from early-stage evidence. A finding replicated across large studies is treated differently from a single small trial, and we say which is which.
- We state the limits of phone-based measurement plainly — motion, lighting, skin perfusion, and sensor quality all affect accuracy.
- Trend over single readings. Nearly every metric here is more meaningful as a pattern over days and weeks than as one isolated number.
- Wellness framing, not diagnosis. See the Privacy Policy and each app's own disclaimer for specifics.
A note on related reading
SmartDeviceRx focuses on phone- and camera-based physiological self-tracking. For broader functional-medicine and physiotherapy care, see Akasha Integrative Health & Physiotherapy, a separate clinical practice these tools are informed by.