1. Bailey and Hubert. Productivity Measurement. Lowe and Brydone printers Limited, Thetford, Norfolk, Great Britain, 1980. vol. ed. (213); 2016. p. 5
2. Chatterjee B, Singh KK, Goswami NG. Fly ash utilization for value added products, February, 1998. Hong Kong: AME Publishing; 2014. p.1-12.
3. Das, A K. Coal ash utilization: An alternative technology, Journal of CAII, September,1999. College Park (MD)]: University of Maryland; 2008. p. 174.
4. Enofe M G. Maintenance impact on Production Profitability - A Case Study, Spring 2010. [dissertation], College Park (MD): University of Maryland; 2008. p. 56.
5. Gunasekaran A. Improving productivity and qual- ity in manufacturing organizations. Int J Prod Econ. 2019; 36:169-83. https://doi.org/10.1016/0925- 5273(94)90022-1