Answer: Casing is designed to deform with movement of the adjacent ground or structure. The useful life of the casing ends when casing curvature forces the inclinometer probe out of the grooves in the casing. Continued movement of the ground pinches or shears the casing, and eventually prevents passage of the inclinometer probe. Large diameter casing (85 mm, 3.34 inch) is suitable for landslides and long term monitoring. It is also appropriate for monitoring multiple shear zones or very narrow shear zones. Large diameter casing is required when the horizontal probe is used. Medium diameter casing (70 mm, 2.75 inch) is suitable for construction projects. It can also be used for slope stability monitoring when only a moderate degree of deformation is expected. Small diameter casing (48 mm, 1.9 inch) is suitable for applications where small deformations are distributed over broad zones. It is generally not installed in soils. Read more about casing curvature and tracking.