Siemens Brothers & Co. Ltd. portable voltmeter, London. A large analogue electrical measuring instrument designed for measuring voltage in power systems and electrical installations. The instrument features a wide volt scale up to approximately 150 volts and is housed in a wooden carrying case for transport and field use. Used by electrical engineers, power station staff, and maintenance technicians when testing circuits and generators. Early–mid 20th century, c.1920s–1940s.
