AVOmeter is a British trademark for a line of multimeters and electrical measuring instruments; the brand is now owned by the Megger Group Ltd.
The first Avometer was made by the Automatic Coil Winder and Electrical Equipment Co. in 1923, and measured direct voltage, direct current and resistance. Possibly the best known multimeter of the range was the Model 8, which was produced in various versions from May 1951 until 2008; the last version was the Mark 7.
The multimeter is often called simply an AVO, because the company logo carries the first letters of 'amps', 'volts' and 'ohms'. The design concept is due to the Post Office engineer Donald Macadie, who at the time of the introduction of the original AVOmeter in 1923 was a senior officer in the Post Office Factories Department in London.
AVO multimeters were almost ubiquitous in British manufacturing and service industry, research and development and higher and further education. They were also widely used by utilities, government agencies and the British armed forces. A number of special versions were produced to British Admiralty and Air Ministry specifications and for other customers.
The Model 8 Marks V, 6 & 7 were designed to meet a NATO specification and were standard issue to NATO services. Many commercial and military service manuals specified that values for measurements of current or voltage had been made with a Model 7 or Model 8 AVOmeter. Advertisements of the late 1930s compared the utility of the AVOmeter to the slide rule. Even today it can still be found in regular use not just with hobbyists but in real life industrial settings..
The analogue AVOs are beautifully engineered - with the highest standards of electrical construction being displayed right up to the Avo 8 Mk5 at which point flexiboards were introduced. As you can see from the following photograph, the AVO works was a colourful place indeed: -