fps calculation with while loop in coroutine

Hi, ım trying to call 24times per 1 second but something is wrong.My test code like this;

 int frame;
 bool stop;

 void Start ()
 {
     StartCoroutine (Test ());
 }

 IEnumerator StopTest ()
 {
     yield return new WaitForSeconds (10f);
     stop = true;
 }

 IEnumerator Test ()
 {
     StartCoroutine (StopTest ());
     while (!stop) {
         frame++;
         yield return new WaitForSeconds (1f / 24f);
     }

     Debug.Log (frame / 24f);
 }

ı should see always "10" on console but my results are like this;

first try 7.583333 second 7.25 7.625...

i dont know what is wrong