Unity3D: Two objects with the same script - unity3d

Question

I would like to associate the same script to different empty objects I just use as placeholders in the game. The aim is to exploit their positions so that when the user touch a point in the screen, close to one of these objects, a dedicate GUI appears. The problem is that though the two objects are different their scripts seem to influence each other so that when the game is running and I touch one of these two objects both the gui appears. What am I doing wrong?
....
private var check: boolean;
var topCamera : Camera;
var customSkin : GUISkin;
function Update () {
if (Input.GetMouseButtonDown(0)){
if(Input.mousePosition.x > this.transform.position.x - Screen.width*0.20 && Input.mousePosition.x < this.transform.position.x + Screen.width*20){
if(Input.mousePosition.y > this.transform.position.y - Screen.height*0.2 && Input.mousePosition.y < this.transform.position.y + Screen.height*0.2){
check = true;
}
}
}
if(check){
//the camera zooms forward
}else{
//the camera zooms backward
}
}
function OnGUI () {
if (this.check){
var w = Screen.width;
var h = Screen.height;
var bw = 0.083;
var bws = 0.001 *w;
GUI.skin = customSkin;
GUI.Box(new Rect(w*0.6,h*0.3,w*0.38,h*0.45), "Stuff");
customSkin.box.fontSize = 0.04*h;
customSkin.textField.fontSize = 0.08*h;
customSkin.button.fontSize = 0.04*h;
textFieldString = GUI.TextField (Rect (w*0.62, h*0.39, w*0.34, h*0.1), textFieldString);
if (GUI.Button (Rect (w*0.62,h*0.50, w*bw, h*0.1), "+")) {
if (this.check){
this.check=false;
}else{
this.check = true;
}
//...
}
//...
}

Answer 1

This is probably not working, because you are comparing apples with oranges in your Update() function. Input.mousePosition returns the the position in 2D pixel coordinates and transform.position returns the GameObject's position in 3D world coordinates.
To check if you clicked on an object, you need to attach a Collider to the game object in question and test for collisions using a Raycast in your script. Here is the relavant example from the documentation in JavaScript:
var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
if (Physics.Raycast (ray, 100)) {
print ("Hit something");
}
The cool thing about this approach is that we are checking for collisions between the Collider and the ray. If you only want to see if you clicked near the GameObject, just make the Collider larger than the GameObject. No need for messing around with inequalities!

Answer 2

If your objective is to click somewhere close to the object and not only at the object, then you have some configurations (positions of those objects in space) where there are space that are close enough to both objects for their GUI to appear and therefore you need some script to decide which one is closer.
I suggest you to implement a monobehaviour that is a singleton that would track those clicks and measure the distance of all objects, to get the closest.
Reading again your post, I think you want to get the GUI just when you click at the object, and when you do this you get both GUIs. I think that's happening because wrong calculation of the area that makes check to go true.
Can you give more details? Is there some space where there shouldn't have GUI messages when clicked, or is everything filled by those objects?