An altimeter test is easiest to understand as a comparison between two heights. Relative altitude describes movement from a starting reference, while absolute altitude uses a different reference and may not be available on every device.
Test a change of floor
- Open Hardware → Altimeter in Device Status⁺.
- Stay on one floor until the readings settle.
- Note the altitude source and the change shown for the current visit. Barometric altitude is used when available; GPS is the fallback.
- Walk up one flight of stairs safely, then stop to read the screen.
- Return to your starting floor and compare the relative reading.
Keep your attention on the stairs while moving. Read the phone only after stopping.
Why does it start near zero?
A relative reading can begin near zero because it measures change since the current reference. It does not mean your home is at sea level. Moving higher should normally produce a positive change relative to that starting point.
Short-term noise and gradual drift are possible. Weather and indoor air pressure affect pressure-derived height, and a floor is not a standardized height. Avoid treating one staircase as a precision calibration fixture.
What if values do not appear?
Check location access as well as any Motion & Fitness permission request. With GPS as the source, a small change of floor may be hidden by vertical positioning uncertainty. Unsupported data should remain untested rather than being recorded as a failure.
The barometer guide explains the underlying pressure check.
Ready to try it?
Device Status⁺ · Monitor and test your iPhone hardware
Free on the App Store