anchor.diff:  
   
     /**
  -   * Returns wether the [StopWatch] is currently running.
  +   * Whether the [StopWatch] is currently running.
      */
  -  bool get isRunning => _start != null && _stop == null;
  -
  -  /**
  -   * Cached frequency of the system. Must be initialized in [_initTicker];
  -   */
  -  static int _frequency;
  +  bool get isRunning => _stop == null;
   
     /**
      * Initializes the time-measuring system. *Must* initialize the [_frequency]
  
positive.code:    * effect.
     */
    void stop() {
      if (!isRunning) return;
      _stop = _now();
    }
  
    /**
  
negative.code:    * This method does not stop or start the [Stopwatch].
     */
    void reset() {
      _start = _stop ?? _now();
    }
  
    /**
     * The elapsed number of clock ticks since calling [start] while the
     * [Stopwatch] is running.
     *
     * This is the elapsed number of clock ticks between calling [start] and
     * calling [stop].
     *
     * Is 0 if the [Stopwatch] has never been started.
     *
     * The elapsed number of clock ticks increases by [frequency] every second.
     */
    int get elapsedTicks {
      return (_stop ?? _now()) - _start;
    }
  
    /**
     * The [elapsedTicks] counter converted to a [Duration].
     */
    Duration get elapsed {
      return new Duration(microseconds: elapsedMicroseconds);
    }
  
    /**
     * The [elapsedTicks] counter converted to microseconds.
     */
    int get elapsedMicroseconds {
      return (elapsedTicks * 1000000) ~/ frequency;
    }
  
    /**
     * The [elapsedTicks] counter converted to milliseconds.
     */
    int get elapsedMilliseconds {
      return (elapsedTicks * 1000) ~/ frequency;
  