inclinometer casings are made of ABS pipes with four orthogonal grooves running longitudinally along its inside surface with a spiral control of less than 1/3° per 3 meters of casing. When installed in a borehole, one set of grooves is aligned in the anticipated direction of movement. The grooves act as guides for the wheels of the inclinometer probe, maintaining the orientation of the probe as it traverses the casing.
Spiral surveys may be performed on deep installations, or where high accuracy is critical. Spiral data allows inclinometer data to be corrected for twisting of the casing that may occur during installation.