MK 



BK 



FIG. it8 MK, magneto key RO, ring-off drop ; BK, battery key ; T, test ; TS, answering 

 switch ; TR, transmitter ; CK, connecting and calling key ; R, receiver ; RC, right-hand 

 cord ; TB, transmitter battery ; LC, left-hand cord ; cc, connection counter ; u, magneto 



