Framerate counter

I have made/found a simple framerate counter, but the weird thing is the result, it is not the same as the stats give in the fps section.

 var updateInterval : float = 0.5;
 
 private var frames : int; // Frames drawn over the interval
 private var timeleft : float; // Left time for current interval
 private var accum : float;
 var highestFPS : float;
 var fps : float;
  
 function Update() {
     timeleft -= Time.deltaTime;
     frames++;
     accum += Time.timeScale/Time.deltaTime;
     
     if(timeleft <= 0.0) {
         fps = accum/frames;
         if (fps > highestFPS) {
             highestFPS = fps;
         }
         accum = 0.0f;
         timeleft = updateInterval;
         frames = 0;
     }
 }