The rod extensometer monitors changes in the distance between one or more downhole anchors and a reference head at the borehole collar. Components of a rod extensometer include anchors, rods with protective tubing, and a reference head. The anchors, with rods attached, are installed downhole. The rods span the distance between the anchors and the reference head, which is installed at the borehole collar. Measurements are obtained at the reference head with a sensor or a depth micrometer, either of which measures the distance between the top (near) end of the rod and a reference surface.

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