This is a bubble level for the Pebble watch. It measures the angle between horizontal and the accelerometer (assumed to be parallel to the bottom of the watch).

Pressing UP or DOWN in the display changes the display style. Currently there are two display styles: bubble and crosshair.

Press SELECT to change settings.

This app should be used when stationary. You may get misleading readings if the watch is moving or experiencing heavy vibration.

There is a setting to turn on the backlight as long as the app is running, for use in dark areas. This feature drains your battery quickly, so use it carefully.

Filtering determines the display's smoothness. Slower settings reject vibration and noise better, but make the display respond more slowly.