ISO 18674-3 applies to the measurement of displacements across a measuring line by means of inclinometers carried out for geotechnical monitoring. It is to be applied in conjunction with ISO 18674-1:2015. NOTE This document fulfils the requirements for the performance monitoring of the ground, of structures interacting with the ground and of geotechnical works by the means of inclinometers as part of the geotechnical investigation and testing according to reference[1] and[2]. ISO 18674-3 also refers to deflectometers (see Annex B) to supplement inclinometers for the determination of horizontal displacements across horizontal measuring lines. NOTE In general, there are two independent displacement components acting across measuring lines. Inclinometers allow the determination of the two components for vertical measuring lines. For horizontal lines, inclinometers are limited to the determination of the vertical component only. If applied in conjunction with ISO 18674-2:2016, ISO 18674-3 allows the determination of displacements acting in any direction. Specifically, this part of ISO 18674 applies to: checking geotechnical designs in connection with the Observational Design procedures; monitoring of geotechnical structures prior to, during and after construction (e.g. natural slopes, slope cuts, embankments, excavation walls, foundations, dams, refuse dumps, tunnels); deriving geotechnical key parameters (e.g. from results of pile load tests or trial tunnelling); identification and monitoring of active shear planes in the ground.