The brown color seems to suggest a previous fire in this area - not a real big surprise
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I have seen only one or two of those "A" meters with wiring feeding into a unilet fitting like this. Mostly, they are installed with the terminal area protruding into the top of a service switch of some type.
I'm guessing that the device to the right is a fused main disco with one of those old "rotor" contact disks. This old service really doesn't look too bad (for its age)- its all the ugly stuff that's been cobbled onto it over the years that's disturbing.
Are you doing any more work for them (I hope), other than the card reader?
Mike (mamills)