ASA C39.1-1959

This standard applies to the following kinds of electrical indicating instruments for direct and alternating current, including instruments with prefixes such as micro-, kilo-, etc: (1) Ammeters (2) Voltmeters (3) Wattmeters (4) Varmeters (reactive-volt-ampere meters) (5) Frequency meters (6) Power-factor meters (7) Indicating instruments functioning on the above principles, but indicating derived quantities 1.2 This standard may apply, with suitable exceptions, to instruments constructed for special requirements. For example, ultrasensitive direct-current micro ammeters, high-resistance voltmeters, thermo-milliammeters, thermo-voltmeters of the vacuum-couple type, and instruments with special and unusual ranges. 1.3 This standard does not apply to the following kinds of instruments: (1) Indicating instruments provided with arrangements for curve drawing, contact making, etc (2) Small instruments of types and sizes where the indications are only approximate; for example, small polarized-vane ammeters used on automobiles, battery-charging outfits, etc