This is the biggest bunch of DIY electrical work I've seen in awhile. Maybe you should explain that there's a reason why you (as one who does electrical work) don't operate a gym, and gym owners shouldn't do electrical work.
I've seen old meters a few times before, but this is interesting - having the meter leads in free air down to a conduit body with a special lid.
There are 10 types of people. Those who know binary, and those who don't.
The brown color seems to suggest a previous fire in this area - not a real big surprise .
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?