Coba jelasin Lihat pula dari Pensil dong

Steve Ritter. Pencils and Pencil Lead. Dimuat pula sebagai artikel di Science & Technology, What's That Stuff?. Volume 79 No 42. 15 Oktober 2001. ISSN 0009-2347

Early Office Museum. History of the Lead Pencil

Sedarlah!, Juli 2007, h.13-4, Watchtower Bible and Tract Society of New York, Inc.

Awake!, July 2007, p. 13-4, Watchtower Bible and Tract Society of New York, Inc.

Erwachet! Juli 2007, p. 13-4, Watchtower Bible and Tract Society of New York, Inc.