This tool is dropped through the drill pipe onto a landing ring located at the bottom of a non-magnetic drill collar. The non-magnet drill collar isolates the tool from magnetic interference from the drill pipe. The survey instrument records one record of the direction, angle, gravity tool face, magnetic tool face, and temperature of the well bore. This tool is used to monitor the location of the well bore during drilling. It operates on 5 AA alkaline or 2 AA high temperature lithium batteries and has a temperature limitation of 125°C [257° F] without a Heat Shield. The tool can be set in non-magnetic sensor or timer modes. The tool is available in 1-3/8" (1.0375")OD and 1-3/4" (1.75") OD running gear.