Vu Ngoc Pi,  Optimal Calculation of Partial Transmission Ratios of Four-Step Helical Gearboxes for Getting Minimal Gearbox Length.   journal   = {International Journal of Mechanical and Mechatronics Engineering}, [online]. World Academy of Science, Engineering and Technology.
    January 2008, vol. 13(1). 22 - 25
    [viewed 21 September 2020]. Available from: https://publications.waset.org/pdf/14628.