Christiansen, S. 1981. Grit Lerche and Axel Steensberg: AGRICULTURAL TOOLS AND FIELD SHAPES : Twenty five years of activity by the international secretariat. (International Secretariat for Research on the History of Agricultural Implements. Publication No. 3) . Copenhagen 1980, 107 s., ill., 23 cm, Kr. 60,-. Nationalmuseet. Geografisk Tidsskrift. 81, (jan. 1981).