Swing arm profilometers (SAP) are one of the few options for accurately measuring the shape of large optical surfaces. The data obtained by accurate measurements are essential for the refinement of the manufacturing process and certification of finished products. In this paper, the principle of these devices is described using the example of SAP measuring device supplied to the Joint Laboratory of Optics in Olomouc (JLO) by Zeeko Ltd. Device modifications and new procedures that have simplified the adjustment of the SAP and had a positive impact on the accuracy of the measurements are also presented. Some of these principles and modifications can be applied to other SAP devices, as well. The results of several sample measurements on the SAP device are compared with measurements on Zygo Verifire digital interferometer and Zeiss Contura G2 HTG portal coordinate measuring machine.