Acoustic borehole imaging tools can create the most accurate and detailed caliper logs, using the pulse echo transit times with an independent acoustic measurement of the borehole drilling fluid velocity, but the range of this type of measurement is often limited by the high acoustic attenuation of the drilling fluid.
If the arms of the caliper log follow the grooves of the spiral, it will report too high an average diameter.
Moving in and out of the grooves, the caliper will give erratic or periodically varying readings.
This oval shape can cause a 2-arm caliper log to overestimate the size of the borehole, if its arms get stuck in the long-axis.
The current state of the art is six independent mechanical arms that simultaneous record the radial distance from the center of the tool.