It's been 24 hours so my 67-year-old memory might be faulty, but this is what I recall ...
A-B = 120v
A/B-C = 120V
A-D = 120V
B-D = 0V
A & B are where the wires come into the breaker, C is where the breaker snaps into place and D, as noted, is the bus bar.
