Não informado. (1960). Educators Guide to Free Science Materials. Educators Progress Service.
Παραπομπή σε μορφή Chicago (17η εκδ.)Não informado. Educators Guide to Free Science Materials. Randolph, Wis: Educators Progress Service, 1960.
Παραπομπή σε μορφή MLA (8th εκδ.)Não informado. Educators Guide to Free Science Materials. Educators Progress Service, 1960.
Πρόσοχή: Οι παραπομπές μπορεί να μην είναι 100% ακριβείς.