def start(self):
        """
        Remember the current set of objects as the comparison for all future calls to diff()
        Called automatically on init, but can be called manually as well.
        """
        refs, count, objs = self.collect()
        for r in self.startRefs:
            self.forgetRef(self.startRefs[r])
        self.startRefs.clear()
        self.startRefs.update(refs)
        for r in refs:
            self.rememberRef(r)
        self.startCount.clear()
        self.startCount.update(count)
        #self.newRefs.clear()
        #self.newRefs.update(refs)