Notice how that meter is wired.
120V A-base meters have one current coil, connected between the two outside terminals. The neutral may run across the two inside terminals, or it may be pigtailed. It doesn't really matter, since these terminals need not carry the neutral current.
But here, it looks like the hot(?) goes across both line terminals, and the neutral(?) is pigtailed and jumpered across both load terminals. This must be a 240V A-base meter, but I don't really get how it's wired. I know there is a way to hook up a 240V meter to work on a 120V circuit, but I don't know what it is. The 1961 Sangamo manual doesn't mention it. I suppose you could open the test switch; that would allow you to run both current coils in series, while keeping them isolated from the neutral connection to the voltage coil, but then how would you terminate the neutral? There's no lug for that!
The few two-wire services I've seen have had 240V meters, since the meter would have probably been replaced sometime in the last 40 years, when no 120V meters were available.
OK, now that I look at the pic again, the wire that I thought was the hot ends up on the right-hand terminals of the branch-circuit cutouts, where the white wires of those two modern romex runs are terminated. Can we assume that those white wires are connected correctly (at least according to modern practice), as they bypass the fuses? For that matter, can we assume anything, not being able to hold a voltmeter to a photo?
(One thing that we can see is not connected correctly is that 12/3 homerun. The red and black are connected to separate fuseholders. This is a multi-wire branch circuit, fed from a 120V service!)
I have run a 240V meter on 120V before, and it seemed to register 20% less than the actual demand. It was for a public display, so accuracy wasn't an issue. It just had to turn visibly.
