docs: def trace(self, buffer, start, length=1):
          """Reads the points stored in the channel buffer.
  
          :param buffer: Selects the channel buffer (either 1 or 2).
          :param start: Selects the bin where the reading starts.
          :param length: The number of bins to read.
  
          .. todo::
             Use binary command TRCB to speed up data transmission.
          """
          # TODO: Do not use transport directly.
          query = 'TRCA? {0}, {1}, {2}'.format(buffer, start, length)
          result = self.transport.ask(query)
          # Result format: "1.0e-004,1.2e-004,". Strip trailing comma then split.
          return (float(f) for f in result.strip(',').split(','))