Quick Measuring Tape Unity Editor Script

MeasuringTape.cs

using UnityEngine;
using System.Collections;

public class MeasuringTape : MonoBehaviour {
	public Vector3 target = Vector3.zero;
}

MeasuringTapeEditor.cs

using UnityEngine;
using System.Collections;
using UnityEditor;

[CustomEditor(typeof(MeasuringTape))]
public class MeasuringTapeEditor : Editor {

	void OnSceneGUI() {
		MeasuringTape tape = ((MeasuringTape)target);

		tape.target = Handles.PositionHandle(tape.target, Quaternion.identity);

		Handles.color = Color.white;
		Handles.DrawLine(tape.transform.position, tape.target);

		Handles.BeginGUI();
		GUILayout.BeginArea(new Rect(Screen.width-100, Screen.height-80, 90, 50));
		if (GUILayout.Button("Dist: "+Vector3.Distance(tape.transform.position, tape.target))) {
			tape.target = tape.transform.position;
		}
		GUILayout.EndArea();
		Handles.EndGUI();
	}

	[MenuItem("GameObject/Create Measuring Tape")]
	static void CreateMeasuringTape() {
		GameObject go = new GameObject("_MeasuringTape");
		go.AddComponent<MeasuringTape>();

		if (Selection.activeTransform != null) {
			go.transform.position = Selection.activeTransform.position;
		}

		go.GetComponent<MeasuringTape>().target = go.transform.position;

		Selection.activeGameObject = go;
	}
}