Inaccurate measurements by ruler in unity ARKit

I'm working on an application for room measurement, a ruler of sorts, using the ARKit in Unity3D. For this I am using raycasts to place objects (spheres), against the wall, and calculate the distance between those objects by getting the position of recognized walls, which the ARKit generates.

The problems I have:

• My placed objects are mostly a bit to far away from those ARKit walls.
• Those objects are floating away when I move. So the measurements are not that precise.
• Furthermore i want to create a gaze pointer, which assigns the wall angle and position by its distance

The code (snippet):

Code (CSharp):

1. // generate first point
2.     Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);;
3.     RaycastHit hit;
4.  
5.     if (Physics.Raycast(ray, out hit))
6.     {
7.             if (!arModeWall)
8.         {
9.             if (!continueMeasure)
10.             {
11.                 if (!firstTouch)
12.                 {
13.                     //Debug.Log("FirstDot");
14.                     firstTouch = true;
15.                     doLine = true;
16.  
17.                     if (fromToCalculation != 1)
18.                         fromToCalculation = 1;
19.                     //continueMeasure = true;
20.  
21.                     Vector3 cameraPos = new Vector3(Camera.main.transform.position.x,  Camera.main.transform.position.y, +10);
22.  
23.                     //Create first sphere (nessacary for position)
24.                     GameObject newPoint = Instantiate(distanceMeasuringSphere, hit.point, Quaternion.identity);
25.                     newPoint.transform.parent = distanceMeasuringSphereContainer.transform;
26.                     distanceMeasuringSphereArray.Add(newPoint);
27.  
28.                     //Create first LineRenderer (nessacary for Visuals)
29.                     GameObject newLR = Instantiate(distanceMeasuringLr, distanceMeasuringSphereArray[distanceMeasuringSphereArray.Count - 1].gameObject.transform.position, Quaternion.identity);
30.                     newLR.transform.parent = distanceMeasuringLrContainer.transform;
31.                     newLR.GetComponent<LineRenderer>().SetPosition(0, distanceMeasuringSphereArray[distanceMeasuringSphereArray.Count - 1].gameObject.transform.position);
32.                     distanceMeasuringLineRendererArray.Add(newLR);
33.  
34.                     //Create first Text (nessacary for Distance)
35.                     GameObject newDistanceText = Instantiate(distanceMeasuringText, hit.point, Quaternion.identity);
36.                     newDistanceText.transform.parent = distanceMeasuringTextContainer.transform;
37.                     distanceMeasuringTextArray.Add(newDistanceText);
38.  
39.                 }

It's the best solution I could think of to create a ruler.
But I am open for improvement, Suggestions as well