The borehole extensometer measures the extension (displacement) which takes place with time in a bored hole or in several bored holes in a rock mass. It essentially consists of an anchor grouted in a borehole and a reference plate. They help to accurately measure the distance between the anchor with respect to the reference plate and monitor their relative displacement with passage of time. The change in displacement between the anchor and reference plate is accurately monitored with passage of time. It is usually assumed that the anchor is in stable ground and so any change in the anchor spacing gives information about the settlement of foundation taking place.