Get Accelerometer to rotate 360 degrees

Hello. I'm using the accelerometer to rotate an object in a game so that the object always points upwards (away from the centre of the Earth let's say) no matter what way the phone is rotated around the z-axis. Think of it like a compass the way the needle always points north no matter what way you have the device rotated. I'm coding in C#.

 using UnityEngine;
 using System.Collections;
 
 public class RotateDial : MonoBehaviour {
     
     private Quaternion localRotation; 
     
     void Start () {
         // copy the rotation of the object itself into a buffer
             localRotation = transform.rotation;
     }
     
     void Update () {
         
         localRotation.z = Input.acceleration.x; 
         
             transform.rotation = localRotation;
     }      
     
     void OnGUI() {
         GUI.Box (new Rect (5, 55, Screen.width / 2, 20), "Local z" + localRotation.z); //, Health_bar_GUI);
         GUI.Box (new Rect (5, 80, Screen.width / 2, 20), "Accel x" + Input.acceleration.x); //, Health_bar_GUI);
         GUI.Box (new Rect (5, 105, Screen.width / 2, 20), "transform rot" + transform.rotation); //, Health_bar_GUI);
     }
 }

My problem is that the accelerometer only seems to work across 180 degrees. The rotation translation for the particular axis is 0 when the phone is held in landscape mode but is either -1 or +1 when it's held portrait (+90 degrees) or upside down portrait (270 or -90 degrees) which works correctly for these rotations. When the phone is held beyond 90 but below 270 degrees the game object does not point in the correct direction. I've attached an image to help explain the problem a bit better.

I believe it to be because the rotation translation goes back to 0 when the phone is held in upside down landscape mode (180 degrees).

Does anyone know a solution that will allow the game object to keep pointing in the same direction even if the phone is turned completely upside down? Thanks in advance.