def tally(self, chain):
        """Store the object's current value to a chain.

        :Parameters:
        chain : integer
          Chain index.
        """

        value = self._getfunc()

        try:
            self._trace[chain][self._index[chain]] = value.copy()
        except AttributeError:
            self._trace[chain][self._index[chain]] = value
        self._index[chain] += 1
Store the object's current value to a chain.

        :Parameters:
        chain : integer
          Chain index.