GRAPHIC RECORDING INSTRUMENTS 555 



Instruments like those just described are useful when a 

 moderate accuracy will suffice; for instance, on a set of feeder 

 panels where many instruments must be installed and consider- 



FIG. 339. Curve drawing ammeters, General Electric Co. 



able expense is not justified. If a high degree of accuracy is 

 desired, more complicated arrangements must be used. 



A registering instrument should be capable of operating for a 

 considerable period without attention, for 1 or 2 weeks in 



