def __call__(self, msg=None):
        """Register or print a new message with timing information.
        """
        if self.disable:
            return
        if msg is None:
            msg = str(self._markCount)
        self._markCount += 1
        newTime = ptime.time()
        self._newMsg("  %s: %0.4f ms", 
                     msg, (newTime - self._lastTime) * 1000)
        self._lastTime = newTime