 Moving in and out of the grooves, the caliper will give erratic or periodically varying readings.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 borehole can change to an oval shape after drilling, which can cause the caliper log to overestimate the size of the borehole if its arms get stuck axis.