Portable DC voltmeter by Evershed & Vignoles Ltd. A precision analogue instrument designed for measuring low direct-current voltages, featuring a sensitive moving-coil meter with a fine-scale range and a protective wooden case. The caution label indicates the use of a press key when taking readings, a feature common in laboratory or calibration instruments to prevent damage to the delicate movement. Used by electrical engineers in testing laboratories, workshops, and calibration work during the early development of electrical measurement. Early–mid 20th century, c.1920s–1940s.
