Text UI shakes when being updated with a countdown function

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 
 public class Timer : MonoBehaviour {
 
     public Text TimerLabel;
     public float timer = 10f;
     public float timera;
     void Start () {
         
     }
     
     
     void Update () {
         timer -= Time.fixedDeltaTime;
         
         TimerLabel.text = timer.ToString();
     }
 }

I have an UI text attached to this script and when it updates, it likes to shake a bit. I have tried various optimizations, like new fonts (mono-something font which has letter all in the same size) and trying various options in text object. (Best fit, Align by geometry)

By shaking i mean it goes up and down and some countdowns from 10 to 7 it shakes a bit, from 7 to 2 it doesn't and from 2 to 0 it also shakes a bit.