His main work (since 1932) was on the geoid and its exterior gravity field or geopotential. His aim was to develop hypothesis -free methods for determining both the gravity field and defining vertical datums for large areas. As part of this work, he introduced normal heights, which can be calculated from geopotential numbers (obtained from precise differential levelling) without needing the uncertain value of gravity along the plumb line of a point, i.e., inside the continental crustal rock under the point.