Sain, signalau - a'r teleffon
By: golygwyd gan BrianNicoll a Jenny Selfe.
Contributors: Nicoll, Brian.; Selfe, Jenny.; British Telecom.
Series: Deall telathrebu -- llyfr 1
Publisher: British Telecom De Cymru
Published: 1988
Language: wel
Number of pages: 22
Subjects: Telecommunication systems.