Calcante, Aldo, Luca Fontanini, and Fabrizio Mazzetto. “Repair and Maintenance Costs of 4WD Tractors and Self Propelled Combine Harvesters in Italy”. Journal of Agricultural Engineering 44, no. s2 (September 8, 2013). Accessed October 30, 2020. https://www.agroengineering.org/index.php/jae/article/view/jae.2013.s2.e70.