Re: AVO Multimeter survey
The Model 7 and Model 40 look very similar on ebay photographs:
both have the mushroom pad switches,
and either screw terminals (Mk I) or sockets (Mk II).
The easiest way to be sure is to ask the vendor for the type number as printed at the top of the instruction plate on the back of the case.
If it's legible, the right hand knob of the Model 7 is much "busier" than on the 40: it has CAPACITY and POWER/DECIBELS segmments astride the DC segment.
If you want a serious, sensitive meter, you'd best go for a Model 8 (Mk I, II, or III). There's a lot of them about on ebay, so they're quite cheap. They have the advantage of high sensitivity, and the benefit of youth (post 1950) - you can still get the correct batteries. I wouldn't go for anything later than the Mk III, because after that one, the internal construction became increasingly flimsy.
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