Turning a Phone Into a Bubble Level

Hanging a shelf without a spirit level usually means eyeballing it, or borrowing an app that's mostly ads. The Digital Bubble Level reads the same accelerometer data a physical bubble level's mechanical wizardry mimics — front-back tilt (beta) and side-to-side tilt (gamma) from DeviceOrientationEvent — and turns it into a bullseye you center by hand.

Why ±0.2° and not 0.0°

No consumer accelerometer reports a mathematically perfect zero at rest; sensor noise and micro-vibration mean the reading jitters by a few hundredths of a degree even on a genuinely flat surface. The tool treats anything inside ±0.2° as "level" so the indicator doesn't flicker between green and not-quite-green while you hold the phone still. It's a usability threshold, not a claim about accuracy — for tolerances tighter than that, a machinist's level or a laser level is the right tool, not a phone.

Getting a clean reading

Lay the phone flat against the actual surface, not propped against something else, and give it a second to settle before reading the bullseye — accelerometer output smooths over a short window internally, so a sudden phone movement briefly overshoots before it stabilizes. Screen protectors and thick cases add their own micro-tilt if they're uneven, so check the reading with and without a case if a hang looks off.

Pairing it with a real reference

For anything load-bearing — shelving brackets, curtain rods, picture frames people will notice — cross-check the phone reading against a physical level's actual bubble before you commit to drilling. If you also need to measure a length while you're at it, the Screen & Physical Ruler calibrates CSS pixels against a real-world object so you get both jobs done from the same tab, and the Digital Compass reads the same sensor family for heading instead of tilt.