the long-axis. In most cases, the borehole's circumference will not be a perfect circle and therefore a caliper tool with several arms is required to obtain a true understanding of the size and shape of the borehole. The current state of the art is six independent mechanical arms that simultaneous record the radial distance from the center of the tool. Abrupt changes in borehole diameter, such as a washout at the bottom of casing, or thin fractures may not be accurately measured due to the geometry or range of the measurement arms. References Petroleum production Well logging