ISO 18674-2:2016 specifies the measurement of displacements along a line by means of extensometers carried out for geotechnical monitoring. General rules of performance monitoring of the ground, of structures interacting with the ground, of geotechnical fills and of geotechnical works are presented in ISO 18674-1. If applied in conjunction with ISO 18674-3, this document allows the determination of displacements acting in any direction. ISO 18674-2:2016 is applicable to: - monitoring the behaviour of soils, fills and rocks; - checking geotechnical designs in connection with the Observational Design procedure; - deriving geotechnical key parameters (e.g. from results of pile load tests or trial tunnelling); - evaluating stability ahead of, during or after construction (e.g. stability of natural slopes, slope cuts, embankments, excavation walls, foundations, dams, refuse dumps, tunnels). 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 extensometers as part of the geotechnical investigation and testing in accordance with References [5] and [6].