The AVOmeter model 2 was a development of the original AVO multimeter which started life back in 1923. You will find more information here about these instruments and other similar models. AVO also produced a range of smaller multimeters which are described here.
AVO Model 2
The model 2 which has a sensitivity of 6mA is a direct descendant of
the original AVO
designed in 1923. I understand that the model 2 started production in
1927, though this one coming from the Douglas Street works must have
been made after 1933. The model 6 which was first made in about 1934/5
is quite a rarity as by that time the firm was also producing the more
versatile universal AC/DC models.
It had a couple of faults when I
received it. The
pointer was bent and tended to stick at half scale and at some time in
the past excessive current had caused the insulation on several of the
wire wound resistors to be charred and the scale had been touched up
with a pen and Indian ink. It came with the battery shown which had
expanded and was very difficult to remove (I have squeezed it in a vice
to put it back for this photograph)
The later model 6 (22 range) with the divide by 2 button, looks much the same as this model 2 except the horse shoe magnet is aligned at right angles to the panel.
Batteries A rectangular 1.5 volt cell with a brass terminal and a flying lead for the negative connection. The 1.5 volt battery can be replaced with a single cell size D to with soldered connections.
How much is it worth? fairly rare Expect to pay £40