Using the extrapolation according to Eq. ( ), the accuracy of NORMALPNO DLPNO-CCSD(T 0 ) with respect to TIGHTPNO DLPNO-CCSD(T 0 ) is in accordance with the results for the individual basis sets. On average, the MAD is only slightly increased, e.g., the MAD of reaction energies amounts to 0.32 kJ • mol -1 for cc-pVTZ, 0.41 kJ • mol -1 for cc-pVQZ, and 0.50 kJ • mol -1 for cc-pV(T,Q)Z. However, although the MADs of the multi-level variant with TIGHTPNO as target accuracy are smaller for the individual basis sets, the accuracy is lower for most of the cases using Table : Mean absolute deviations (MADs) and standard deviations (SDs) in kJ • mol -1 for reaction energies and barrier heights of the proton transfer reactions from the BH9 set with respect to TIGHTPNO DLPNO-CCSD(T 0 ) for the same basis set. Pair-selected multi-level DLPNO-CCSD(T 0 ) with TIGHTPNO and NORMALPNO as target accuracies is compared to NORMALPNO DLPNO-CCSD(T 0 ) for different basis sets as well as for the basis set extrapolation according to Eq. ( ). the extrapolation technique as for the reaction energies calculated with cc-pV(T,Q)Z: the MAD is 0.21 kJ • mol -1 for cc-pVTZ, 0.35 kJ • mol -1 for cc-pVQZ, and 0.63 kJ • mol -1 for cc-pV(T,Q)Z.