Calibrate your phone level on any table

The accelerometer in a phone is tiny and is mounted with a small error. Two phones of the same model can disagree by half a degree. On top of that:

• A case that is thicker at one end tilts the phone.
• A camera bump lifts one corner when the phone lies on its back.
• The sides of a phone are rounded, so it doesn't stand exactly upright on its edge.

That is why a level app that just reads the sensor can show 0.5–1° on a surface that is perfectly level.

Most level apps say: put the phone on a level surface and press Calibrate. But if you had a surface you knew was level, you wouldn't need a level app. Calibrating on a slightly tilted table builds that tilt into every later measurement.

Loodis uses the trick builders use to check a spirit level: measure, turn it around 180° on the same spot, measure again. A real tilt of the table changes sign when the phone turns, the error of the phone does not. The average of the two readings is the phone's own error.

Loodis checks every turn with the gyroscope, speaks each step aloud and tells you if the phone moved. The screen-down steps measure the sensor error for every mode; the back steps add the effect of the camera bump.

When you use the phone on its side or standing on its end, the rounded edges add their own error. With Pro you can calibrate each side and the upright position separately – again by turning the phone around on the same spot, so no level surface is needed.

Put the phone on a table, note the reading, turn it around 180° on the same spot. After a good calibration both readings are the same number with opposite direction. If they are not, run the calibration again on a steadier surface.

Calibrate again after you put on a new case. You can always go back to the factory reading in the calibration screen.