Nalhadi, Ahmad, et al. “Usulan Perbaikan Kualitas Produk Pipa Api 5L PSL2 Menggunakan Metode Six Sigma”. Jurnal INTECH Teknik Industri Universitas Serang Raya, vol. 4, no. 2, Dec. 2018, pp. 77-85, https://doi.org/10.30656/intech.v4i2.1083.