1. “The productivity of several machines under the care of one operator”;ASHCROFT;J. JR. Statist. Soc., B,1950
2. “Determining the number of machines to be attended by an operator in order to minimize the total cost per unit of production”;ANSON;Time and Motion Study,1957
3. F. BENSON, “Machine Interference. A mathematical study of some congestion problems in industry”, Thesis, Birmingham, (1957).
4. “The productivity of machines requiring attention at random intervals”;BENSON;J. R. Statist. Soc., B,1951