Abstract: A highly flexible, wireline survey tool has roller knuckle joints that enable the survey tool string to penetrate and survey horizontal wells having inclinations of about 80° and more from vertical. The survey tool string includes a nose, roller stems, roller knuckle joints, and a highly accurate electronic gauge embedded in a roller cage. Each component has external wheels that are free to contact and roll when they make contact with the inner surfaces of the well. The wheels act as both friction-reducing elements and stand-offs for the survey tool string with respect to the inner surfaces of the well.