Bubble level
The accelerometer senses which way gravity points, so a phone can act as a spirit level. It is genuinely useful for hanging a shelf, and it is limited by how flat the phone itself sits.
| Sensor used | Accelerometer |
|---|---|
| Unit | Degrees from level |
| Useful range | ±90° of tilt on two axes |
| Cannot do | Match a machinist's or engineer's level, where fractions of a degree matter |
The mechanism, not the marketing.
At rest the accelerometer measures one quantity above all: gravity, about 9.81 m/s² pointing down. How that vector is distributed across the phone's three axes tells you exactly how the phone is tilted.
Comparing the axes gives the tilt angle directly, which the display shows as a bubble or a number.
What a phone cannot do here.
- The reference surface is the phone, not the screen. Cases, camera bumps and slightly non-parallel housings all mean the body may not be perfectly aligned with the surface you rest it on.
- Accelerometers have a small bias that varies between devices and drifts with temperature, so two phones on the same surface can disagree slightly.
- Any real movement adds to gravity in the reading, so the phone has to be still for the angle to mean anything.
How accurate is a phone bubble level?
Good enough for shelves, picture frames and furniture — around a degree in practice. Not good enough for machining or precision alignment.
Does my case affect the reading?
It can. The level measures the phone's orientation, so a case that holds the body at a slight angle to the surface shifts the result. Checking with the case off is a quick way to see the difference.
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