Multiferroic materials in which strongly coupled magnetic and ferroelectric order parameters coexist attract considerable interest. Below 90 K, CaMn7O12 possesses the largest magnetically induced polarisation measured to date. With a view to integrate multiferroics in novel technology, understanding the microscopic physics behind this giant polarisation, which has been predicted to be due to exchange-striction between Mn3+ and Mn4+ ions, is of key importance. As described in this proposal, by accurately determining the oxygen positions in CaMn7O12 (impossible with x-ray diffraction techniques) we will be able to determine the potentially critical role of charge disproportionation in creating the electric polarisation. In addition, the collected data would allow a hypothesis of a novel orbital helix method of electronic ordering to be tested, which is thought to occur below 250 K.