Missing a spirit level at home developer Alanceil decided to use the Wiimote as a replacement. Put the Wiimote on a surface you want to use as a reference and press A. This will start a calibration, and afterwards you can put it on a target surface to see its difference in inclination.

Changes:

Chg: Slightly adjusted maximum value to reduce flickering near 90 degrees.
Chg: GRRlib is now responsible for all drawing needs. (Which means: more eye-candy)
Add: Raw acceleration values in the debug info text
Add: Freeze function on pressing Plus to freeze current values – this is interesting if you cannot see your screen.

http://wiibrew.org/wiki/Leveltool