The paper presents two complementary strategies for identifying errors in spreadsheet programs. The strategies presented are grounded on the assumption that spreadsheets are software, albeit of a different nature than conventional procedural software. Correspondingly, strategies for identifying errors have to take into account the inherent properties of spreadsheets as much as they have to recognize that the conceptual models of 'spreadsheet programmers' differ from the conceptual models of conventional programmers. Nevertheless, nobody can and will write a spreadsheet, without having such a conceptual model in mind, be it of numeric nature or be it of geometrical nature focused on some layout.