Hi;
I've been wondering a few times about caclculator model # and I never got to a "pattern", if there is one. And I saw a few at the MoHPC that end with a "6" other than the HP16C (46, 56, 66 and 86), all old fashioned, desktop models. But this called my attention, too.
It's not a rule, but many companies use the last digit in their equipments' model # as sort of an ID for their particular purpose. Three HP calculators with a "7" as the last digit are financial, but the well known 67/97 counterparts are not. Both HP22 and HP12C have their model # ending in "2" and are financial, but the 32, 32S and 42S are not. There are many model # ending with "1", "2", "5", "7" and "8". A few others with "0", "4" and "9" as the last digit. But I saw only the HP33E/C and the HP83 with a "3" in the end.
The fact is that the HP calculators are split in two major groups: financial and scientific. Both have their graphics versions, so I don't thing a graphic calculator belongs to a graphics group, maybe I'm wrong. But the HP16C is a class by itself, and if we take those three desktop, old fashion 46, 56, 66 and 86 off the score, the "6" in the end is also an exclusive ID number.
Cheers.