When core is cut, it is relieved of stress and expands. In a normal coring operation, core is reground by the inner gauge of the core bit causing it to lose some of this out of roundness. To avoid this, Sigra provides core bits that expand internally. In addition, they have created a tool to measure core ovality to micron accuracy. In this, the core is placed on rollers and rotated between two measuring arms. The major and minor diameters may be deduced from this measurement.
Simple elastic analysis can be used to determine the likely difference in the major and minor stresses perpendicular to the core.