We propose to carry out single crystal diffraction measurements of the most hydrated MgSO4 compounds, meridianiite, using a thin-walled TiZr gas cell on SXD up to 5 kbar. These measurements will provide us with the ground-truth for a set of ab initio DFT calculations which predict the variation in, for example, unit-cell dimensions, particular trends in hydrogen bond lengths, and changes in polyhedral compressibilities. The work will complement our earlier single-crystal study of meridianiite at room pressure from 4-250 K, and our high-pressure powder diffraction studies.