code: def ttotdev(data, rate=1.0, data_type="phase", taus=None):
      
  
      (taus, mtotdevs, mde, ns) = mtotdev(data, data_type=data_type,
                                          rate=rate, taus=taus)
      td = taus*mtotdevs / np.sqrt(3.0)
      tde = td / np.sqrt(ns)
      return taus, td, tde, ns
docs: Time Total Deviation
          modified total variance scaled by tau^2 / 3
          NIST SP 1065 eqn (28) page 26  <--- formula should have tau squared !?!