movement. A "Universal" version having additional alternating current and alternating voltage ranges was offered from 1933 and in 1936 the dual-sensitivity Avometer Model 7 offered 500 and 100 Ω/V. Between the mid 1930s until the 1950s, 1,000 Ω/V became a de facto standard of sensitivity for radio work and this figure was often quoted on service sheets. However, some manufacturers such as Simpson, Triplett and Weston, all in the USA, produced 20,000 Ω/V VOMs before the Second World War and some of these were exported. After 1945–46, 20,000 Ω/V became the expected standard for electronics, but some makers offered even more sensitive instruments. For industrial and other "heavy-current" use low sensitivity multimeters continued to be produced and these were considered more robust than the more sensitive types. High-quality analog (analogue) multimeters continue to be made by several manufacturers, including Chauvin Arnoux (France), Gossen Metrawatt (Germany), and Simpson and Triplett (USA). Pocket watch meters Pocket-watch-style meters were in widespread use in the 1920s. The metal case was typically connected to the negative connection, an arrangement that caused numerous electric shocks. The technical specifications of these devices were often crude, for example the one illustrated has a resistance of just 25 Ω/V, a non-linear scale and no zero adjustment on both ranges. Vacuum tube voltmeters Vacuum tube voltmeters or valve voltmeters (VTVM, VVM) were used for voltage measurements in electronic circuits where high input impedance was necessary. The VTVM had a fixed input impedance of typically 1 MΩ or more, usually through use of a cathode follower input circuit, and thus did not significantly load the circuit being tested. VTVMs were used before the introduction of electronic high-impedance analog transistor and field effect transistor voltmeters (FETVOMs). Modern digital meters (DVMs) and some modern analog meters also use electronic input circuitry to achieve high input impedance—their voltage ranges are functionally equivalent to VTVMs. The input impedance of some poorly designed DVMs (especially some early designs) would vary over the course of a sample-and-hold internal measurement cycle, causing disturbances to some sensitive circuits under test. Additional scales Additional scales such as decibels, and measurement functions such as capacitance, transistor gain, frequency, duty cycle, display hold, and continuity which sounds a buzzer when the measured resistance is small have been included on many multimeters. While multimeters may be supplemented by more specialized equipment in a technician's toolkit, some multimeters include additional functions for specialized applications