C# Timer not changing values of doubles

I have a timer set up and enabled for every 100ms. However for the life of me I can't work out why the timer is not changing the double values. It's just staying the same. The timer itself works absolutely fine. I believe it's going to be something simple within the timer_tick code itself.

 private void timer1_Tick(object sender, EventArgs e)
    {
                  
       cords.Text = map.Position.ToString();
        double enemnylat = 51.97840583915594;
        double enemnylng = 0.35796410164283465;
        double friendlylat = 52.19119384412198;
        double friendlylng = 0.93958379542825944;
        PointLatLng enemny = new PointLatLng(enemnylat, enemnylng);
        PointLatLng friendly = new PointLatLng(friendlylat, friendlylng);
        double markerDist = GMap.NET.MapProviders.EmptyProvider.Instance.Projection.GetDistance(enemny, friendly);
       
        if (markerDist == 0)
        {
            miles.Text = "At Destination";
        } else if (markerDist != 0)
        {
            miles.Text = "Miles: " + markerDist.ToString();
            friendlylat = friendlylat - 0.1;
            friendlylng = friendlylng - 0.1;
            if (enemnylat >= friendlylat && enemnylng >= friendlylng)
            {
                friendlylat = friendlylat - 0.1;
                friendlylng = friendlylng - 0.1;

            }
            else if (enemnylat <= friendlylat && enemnylng <= friendlylng)
            {
                friendlylat = friendlylat + 0.1;
                friendlylng = friendlylng + 0.1;
            }
        }
      

    }