Abstract: There is provided an apparatus for measuring linear movement of an ice mass on a body of water. The apparatus comprises two stationary anchors on the floor of the body of water. Two sheathed cables attached to the anchors extend from the anchors through a downtube in the ice mass to spring-loaded reels located above the ice mass. The spring-loaded reels are coupled to multi-turn potentiometers. The downtube comprises a pipe and two cable guide structures disposed therein. The guide structures are oil filled to afford smooth axial movement of the cables through the downtube as the ice mass and the downtube carried thereby move relative to the anchors.