anchor.diff:     * This method does not stop or start the [Stopwatch].
      */
     void reset() {
  -    if (_start == null) return;
  -    // If [_start] is not null, then the stopwatch had already been started. It
  -    // may running right now.
  -    _start = _now();
  -    if (_stop != null) {
  -      // The watch is not running. So simply set the [_stop] to [_start] thus
  -      // having an elapsed time of 0.
  -      _stop = _start;
  -    }
  +    _start = _stop ?? _now();
     }
   
     /**
  -   * Returns the elapsed number of clock ticks since calling [start] while the
  +   * The elapsed number of clock ticks since calling [start] while the
      * [Stopwatch] is running.
      *
  -   * Returns the elapsed number of clock ticks between calling [start] and
  +   * This is the elapsed number of clock ticks between calling [start] and
      * calling [stop].
      *
  -   * Returns 0 if the [Stopwatch] has never been started.
  +   * Is 0 if the [Stopwatch] has never been started.
      *
      * The elapsed number of clock ticks increases by [frequency] every second.
      */
     int get elapsedTicks {
  -    if (_start == null) {
  -      return 0;
  -    }
  -    return (_stop == null) ? (_now() - _start) : (_stop - _start);
  +    return (_stop ?? _now()) - _start;
     }
   
     /**
  -   * Returns the [elapsedTicks] counter converted to a [Duration].
  +   * The [elapsedTicks] counter converted to a [Duration].
      */
     Duration get elapsed {
       return new Duration(microseconds: elapsedMicroseconds);
     }
   
     /**
  -   * Returns the [elapsedTicks] counter converted to microseconds.
  +   * The [elapsedTicks] counter converted to microseconds.
      */
     int get elapsedMicroseconds {
       return (elapsedTicks * 1000000) ~/ frequency;
     }
   
     /**
  -   * Returns the [elapsedTicks] counter converted to milliseconds.
  +   * The [elapsedTicks] counter converted to milliseconds.
      */
     int get elapsedMilliseconds {
       return (elapsedTicks * 1000) ~/ frequency;
  
positive.code:    * If the [Stopwatch] is currently running, then calling start does nothing.
     */
    void start() {
      if (isRunning) return;
      if (_start == null) {
        // This stopwatch has never been started.
        _start = _now();
      } else {
        // Restart this stopwatch. Prepend the elapsed time to the current
        // start time.
        _start = _now() - (_stop - _start);
        _stop = null;
      }
    }
  
negative.code:    * effect.
     */
    void stop() {
      _stop ??= _now();
    }
  
    /**
  