EL beam sensors are used to monitor differential movement and rotation in structures. Typical applications include:

• Monitoring stabilization measures, such as pressure grouting and underpinning.
• Monitoring structures which may be affected by nearby tunneling and excavating.
• Evaluating the performance of bridges and beams under load.
• Monitoring the stability of structures in landslide areas.
• Monitoring the deflection and deformation of retaining walls.
• Monitoring convergence and other movements in tunnels

Source: http://www.slopeindicator.com/instruments/tilt-elbeam.php

Link to report of this instrument: ELB