The Sailwave results list 3 modifications, MN B SP. The MN mod (only 0.995) implies that the main is different (square vs pin) but of the SAME AREA, not larger as in the previous calc. Mr. Bill, what are those areas, anyway?

There is no "B" in the tables but if it's really "BM" (sic) then that is 0.995. The SP is the spinnaker at 0.96. That leaves us at

73.0 x 0.995 x 0.995 x .096 = 69.4

Where did the 70.2 come from? If you put in a "fat boy" H3 at 1.01 it gets closer. Were they...chubby?

Granted, it's a small difference but one wonders. Whenever Portsmouth is used I think of the priest saying, "Let us proclaim the mystery of Faith."