Acceleration and accelerometer calibration

In my game I move a sphere using the accelerometer. I calibrate it with the matrix4x4 method I saw in another thread (link: http://answers.unity3d.com/questions/927515/accelerometer-calibration-2.html)

I need something similar but it must work only in x and z axis. So I tried to edit it and this is the result.

 void Calibrate()
     {
         Vector3 wantedDeadZone = new Vector3(Input.acceleration.x, 0, Input.acceleration.y);
         Quaternion rotateQuaternion = Quaternion.FromToRotation(new Vector3(0f, 0f, -1f), wantedDeadZone);
         
         //create identity matrix ... rotate our matrix to match up with down vec
         Matrix4x4 matrix = Matrix4x4.TRS(Vector3.zero, rotateQuaternion, new Vector3(1f, 1f, 1f));
         //get the inverse of the matrix
         calibrationMatrix = matrix.inverse;
     }
 
 //returns the "calibrated" acceleration
 Vector3 getAccelerometer(Vector3 accelerator)
     {
         Vector3 accel = calibrationMatrix.MultiplyVector(accelerator);
         return accel;
     }
 
 void FixedUpdate()
     {
         Vector3 rawAccel = new Vector3(Input.acceleration.x * speed, 0, Input.acceleration.y * speed);
             Vector3 movement = getAccelerometer(rawAccel);
             rb.AddForce(movement);
    }

The calibration works great on the y axis but it doesnt't work on the x axis. The "calibrated" acceleration on the x axis is 0 when the phone is on flat, like on a table.

How can I fix this problem?

Thanks in advance and sorry for my bad English