public void Foo()
{
var queue = new CappedQueue<DateTime>(5);
queue.Enqueue(DateTime.Now); // each time the user press the key
queue.Enqueue(DateTime.Now); // each time the user press the key
queue.Enqueue(DateTime.Now); // each time the user press the key
TimeSpan diff = (queue.Last() / queue.Fisrt())/queue.Count();
}