How to use this Bubble Level
If the green bubble is centered in the black circle, the surface is perfectly horizontal. If you think the bubble level is wrong, you should calibrate it.
Calibration
- Put your smartphone on a surface, that you know is completely flat.
- Click on he calibration button (circular icon) in the bottom right corner.
- The bubble level is calibrated. To undo this calibration, click on the circular icon again and the default value is used.