To overcome the limitations of conventional interferometry, a technique has been developed which allows the absolute topography measurement of near-plane and slightly curved optical surfaces of arbitrary size with low measurement uncertainty. The Extended Shear Angle Difference (ESAD) method combines deflectometric and shearing techniques in a unique way to minimize measurement errors and to optimize measurand traceability. A device for the topography measurement of optical surfaces up to 500 mm in diameter, achieving sub-nanometer repeatability, reproducibility and uncertainty, was built at the Physikalisch-Technische Bundesanstalt (PTB). The ESAD method is optimally suited for creating a primary standard for straightness and flatness with highest accuracy by which the three-flat test or liquid mirrors can be replaced as starting points of the traceability chain in flatness measurement. In the following, the improved ESAD device which uses optimized opto-mechanical components is presented. Central aspects of the proper design and use of deflectometric systems are highlighted, including the optimal use of pentaprisms.