Nice pictures, Jwww.
I'm not familiar with these panels, but it appears from the second picture to be a main lug panel where the top portion is used for 240-volt circuits, and the lower right breaker is feeding the bottom half of the panel for the 120-volt loads.
This reminds me of the comments made by harold endean in the General Discussion section. The thread is "arrangement of breakers" and he comments on the overheating of the buss with large loads sharing the buss. Here we have what looks like a "main" breaker feeding the lower half of the panel with a water heater breaker sharing the buss.
Dave