This article describes a measuring method used for monitoring deformations in wooden grating mining casings. It is intended, in particular, to determine the degree of deflection of load-bearing elements in relation to their original position. It was prepared especially to supplement the technical evaluation of wooden supporting casings in historic mines, underground sections of tourist routes, tunnels etc. The primary reason for the development of this problem were the designs prepared in recent years for large-scale grating constructions at Wieliczka Salt Mine and those for their reconstructions (strengthenings). The article describes the assumptions for the method proposed as well as the measurement system prepared. At Wieliczka Salt Mine two chambers with grating casings were selected and these were equipped with measuring devices. This paper presents the characteristics of these structures, the distribution of the devices installed and the course of the measuring process.