Signal Training Volume III, Pamphlet No. 4, Switchboard Field 10 Line Mark 236, 1929
From RCSigs.ca
The Signal Training Volume III, Pamphlet No. 4, Switchboard Field 10 Line Mark 236, 1923 Reprint with Amendment 1 1929 was issued by the War Office. The pamphlet is 20 pages long and gives a general description of the set, a technical description, operating instructions and detailed instructions for connecting the unit.