"PS Magazine: 50 years of PM"(PDF). PS, the Preventative Maintenance Monthly (pdf) (583): 5. Archived(PDF) from the original on October 23, 2023. Retrieved October 23, 2023.
"PS Magazine: 50 years of PM"(PDF). PS, the Preventative Maintenance Monthly (pdf) (583): 5. Archived(PDF) from the original on October 23, 2023. Retrieved October 23, 2023.