IMPORTANT (please read before ordering): The compass needs to be leveled in order to give an accurate reading. The angle the compass makes with the ground will depend on the angle of your head tube and the grade of the terrain your are riding on. Bumps, bouncing and road vibes will normally make the compass align correctly while riding, but a steep grade or a sharper head tube angle may cause it to do so more slowly. The only true way to ensure an accurate reading is to level the compass.