Standard atmospheric pressure at sea level is 1013.25 hPa (also written 29.92 inHg). The number varies on three timescales: weather (a few hPa over hours, large drops before storms), altitude (about 12 hPa per 100 m), and very long-term geophysical (decades). The sensor reports it because the same data drift powers a number of useful behaviors.
Most usefully, sustained pressure drops of more than 6 hPa over a few hours reliably precede precipitation; rapid rises follow it. Indoor pressure tracks outdoor pressure almost exactly, so the sensor is a free barometer.
Pressure changes also have direct human effects. Mukamal et al. found measurable correlations between sudden barometric drops and migraine onset. Sinus pressure, joint pain in osteoarthritis, and sleep-disordered breathing have similar weaker associations. For people who respond to weather changes, watching the sparkline turn down is genuinely actionable.
The sensor uses a Bosch BMP390L with ±0.5 hPa absolute accuracy and very low noise: well below the threshold of any human-relevant change.
References
- NOAA JetStream - Atmospheric pressure www.weather.gov
- Bosch - BMP390L pressure sensor datasheet www.bosch-sensortec.com
- Mukamal et al. - Weather and migraine pubmed.ncbi.nlm.nih.gov
- Pressure changes and sleep-disordered breathing doi.org
