Editing Multimeter (section)

=== Avometer ===
[[File:AVO Model 8 Mk7 P4 by Megger.jpg|thumb|upright|[[Avometer]] Model 8]]
The invention of the first multimeter is attributed to British Post Office engineer, Donald Macadie, who became dissatisfied with the need to carry many separate instruments required for maintenance of [[telecommunication circuit]]s.<ref>{{cite web|url=http://www.glias.org.uk/news/237news.html |title=Greater London Industrial Archaeology Society |access-date=2010-11-02 |work=glias.org.uk}}</ref><!--(The statement that Mr MaCadie became dissatisfied with having to carry many separate instruments is questionable. At the time when the Original Avometer patent (GB200977, 1923) was granted, he was manager of the Post Office factory in Holloway, London and 50 years old. If he still had occasion to use meters in his work, he would very likely have had an assistant to carry them for him; he may have been very considerate towards his assistants.]<ref>Obituary Wireless World, April 1955</ref>--> Macadie invented an instrument which could measure [[amperes]] (amps), volts and [[ohm]]s, so the multifunctional meter was then named [[Avometer]].<ref name="Grace_AVO">{{cite web |url=https://www.gracesguide.co.uk/Avo |format=[[MediaWiki]] |website=gracesguide.co.uk |title=AVO |access-date=2010-11-02}}</ref> The meter comprised a moving coil meter, voltage and precision resistors, and switches and sockets to select the range.

The first Avometer had a [[Sensitivity (electronics)|sensitivity]] of 60&nbsp;Ω/V, three direct current ranges (12&nbsp;mA, 1.2&nbsp;A, and 12&nbsp;A), three direct voltage ranges (12, 120, and 600&nbsp;V or optionally 1,200&nbsp;V), and a 10,000&nbsp;Ω resistance range. An improved version of 1927 increased this to 13 ranges and 166.6&nbsp;Ω/V (6&nbsp;mA) 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&nbsp;Ω/V.<ref>Advertisement – The Electrician, 1 June 1934</ref> Between the mid-1930s until the 1950s, 1,000&nbsp;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 US, produced 20,000&nbsp;Ω/V VOMs before the Second World War and some of these were exported. After 1945–46, 20,000&nbsp;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.

The Automatic Coil Winder and Electrical Equipment Company (ACWEECO), founded in 1923,  was set up to manufacture the Avometer and a coil winding machine also designed and patented by MacAdie. Although a shareholder of ACWEECO, Mr MacAdie continued to work for the Post Office until his retirement in 1933. His son, Hugh S. MacAdie, joined ACWEECO in 1927 and became Technical Director.<ref>Imperial College Library Archives – Papers of Donald Macadie 1871–1956 MS2015/21</ref><ref>The Electrician 15 June 1923, p. 666</ref><ref name="Grace_AVO" /> The first AVO was put on sale in 1923, and many of its features remained almost unaltered through to the last Model 8.