Acceleration problem with Fake Gravity.

Hello guys, I am following this tutorial https://www.youtube.com/watch?v=gHeQ8Hr92P4 in order to make a similar game. My game will have a planet and the user will control a character who moves on it, as you can see in the video. The point is, that i want to test the game in mobile devices (Windows phone), so i have to use acceleration/gyroscope. I used this line of code for the player's movement: "transform.Translate(Input.acceleration.x, 0, -Input.acceleration.z); ". It works but my problem is that if i hold the device still on the ground to play, the player object keeps moving forward on the planet with high speed, so i have to lift and rotate the device up in the air in order to control the movement correctly. What can i do so i can control the player's movement correctly while holding the mobile device properly ? Thanks in advance.