Issafira, Radissa Dzaky, et al. “The Effect of Coal and Sawdust Co-Firing on Boiler Efficiency With the Direct and Indirect Calculation Methods at PT PLN Nusantara Power Unit 2”. Jurnal Rekayasa Mesin, vol. 20, no. 2, Aug. 2025, pp. 319-28, doi:10.32497/jrm.v20i2.6548.