"John T" wrote
For instance, every W&B graph I've seen (Skyhawks, Skylanes,
C150s, Warriors, Katanas, Tomahawks - all under 35 years old)
have shown this graph using only weight/moment. All the sample
loading problems I've seen have all used moment instead of arm,
too.

In those airplanes, the "arm" is generally fixed by the location
of the seats and bagage compartment. On the graphs, the upward
sloping lines each represent a different arm. Regardless of how
it is presented, a w/b calculation always involves weights and
arms. Moment is simply weight times the arm.

Bob Moore