The RST Digital MEMS Inclinometer Spiral Sensor is used to determine down-hole helical deformation of installed inclinometer casing. Installed casing spiral is a function of the manufacturing process, casing coupling, and installation technique.

Best casing installation practice requires that the casing be installed with the correct azimuth from the start and throughout the installation, with no torque applied either intentionally or otherwise during the installation. Such carefully installed RST inclinometer casing would typically maintain groove azimuth to within a few degrees over 30 metres. However, for very deep installations, or installations where twist due to installation problems is suspected, the Digital MEMS Inclinometer Spiral Sensor permits measurement of the installed groove azimuth down-hole.