If neutrinoless double beta decay were to be observed, its half life would provide a determination of the effective neutrino mass as long as the nuclear matrix element can be determined. These matrix elements are not directly sampled by any other physical process and their values, which are by necessity taken from theoretical calculations, are rather uncertain. However, various elements of these calculations can be benchmarked against measureable nuclear properties. Using the 76Ge➞76Se system, we have determined the occupancy of protons and neutrons in the ‘active orbitals’ of the respective 0+ ground states, and the difference between them, thus characterising the ground-state wave functions. The Fermi surface was found to be more diffuse than previous calculations suggested. Pairing properties have also been studied to test the validity of the BCS approximation used in QRPA, one of the major theoretical approaches to calculating the matrix elements. We are continuing this programme by studies of the 130Te➞130Xe and 100Mo➞100Ru systems, where each presents a different experimental challenge. An overview of the programme and its impact will be discussed.