How to measure section of environment in unity editor using mouse cursor?

I just made a simple Editor overriding EditorTool.

If enabled, when user holds the left shift button, the editor draws a line and shows the size:

[EditorTool("Ruler Tool")]
public class RulerTool : EditorTool
{
    VisualElement _toolRootElement;
    bool _downEvent;
    bool _upEvent;

    private Vector3 _startPosition;

    public override void OnActivated()
    {
        _toolRootElement = new VisualElement();
        _toolRootElement.style.width = 200;
        var backgroundColor = EditorGUIUtility.isProSkin ? new Color(0.21f, 0.21f, 0.21f, 0.8f) : new Color(0.8f, 0.8f, 0.8f, 0.8f);
        _toolRootElement.style.backgroundColor = backgroundColor;
        _toolRootElement.style.marginLeft = 10f;
        _toolRootElement.style.marginBottom = 10f;
        _toolRootElement.style.paddingTop = 5f;
        _toolRootElement.style.paddingRight = 5f;
        _toolRootElement.style.paddingLeft = 5f;
        _toolRootElement.style.paddingBottom = 5f;
        var titleLabel = new Label("Ruler Tool");
        titleLabel.style.unityTextAlign = TextAnchor.UpperCenter;


        _toolRootElement.Add(titleLabel);
        var sv = SceneView.lastActiveSceneView;
        sv.rootVisualElement.Add(_toolRootElement);
        sv.rootVisualElement.style.flexDirection = FlexDirection.ColumnReverse;

        SceneView.beforeSceneGui += BeforeSceneGUI;
    }

    public override void OnWillBeDeactivated()
    {
        _toolRootElement?.RemoveFromHierarchy();
        SceneView.beforeSceneGui -= BeforeSceneGUI;
    }

    void BeforeSceneGUI(SceneView sceneView)
    {
        if (!ToolManager.IsActiveTool(this))
            return;


        if (Event.current.type == EventType.KeyDown && Event.current.keyCode == KeyCode.LeftShift)
        {
            if (!_downEvent)
                _startPosition = GetCurrentMousePositionInScene();

            _downEvent = true;
            Event.current.Use();
        }
        else if (Event.current.type == EventType.KeyUp && Event.current.keyCode == KeyCode.LeftShift)
        {
            _downEvent = false;
            Event.current.Use();
        }
    }

    public override void OnToolGUI(EditorWindow window)
    {
        if (!(window is SceneView))
            return;

        if (!ToolManager.IsActiveTool(this))
            return;


        if (_downEvent)
        {
            float distance = Vector3.Distance(_startPosition, GetCurrentMousePositionInScene());
            Handles.Label(GetCurrentMousePositionInScene() + new Vector3(0, 0, 0.7f), distance.ToString());
            Handles.DrawLine(_startPosition, GetCurrentMousePositionInScene());
            Handles.DrawWireDisc(GetCurrentMousePositionInScene(), Vector3.up, 0.5f);
        }

        window.Repaint();
    }

    Vector3 GetCurrentMousePositionInScene()
    {
        Vector3 mousePosition = Event.current.mousePosition;
        var placeObject = HandleUtility.PlaceObject(mousePosition, out var newPosition, out var normal);
        return placeObject ? newPosition : HandleUtility.GUIPointToWorldRay(mousePosition).GetPoint(10);
    }
}