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Full Version: Re: Richard Nelson's pictures of the 4 HP 15c versions
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The capital C stands for 100 in roman numerals, which is about the relative increase in speed of the new 15C's compared to the old ones. For me it should therefore be a capital C (still) much like the V and X represented the memory-increase (in roman numerals) of the 41CV and 41CX models compared to the 41C.

"C" in HP calculator convention stands for continuous in terms of memory. The first models were not able to maintain the memory once they were switched off. I am not sure whether the HP-19C/29C or the HP-25C were the first to have the continuous memory feature. Apparently, this feature was a big enough differentiator for the marketing guys to use the C for the HP-41, the voyager series and even the HP-28C. Yet later, with the HP-28S which got more memory the C has been abandoned, and only S (for scientific) and B (for business) survived in the more recent models.

And I speculate that the C was in upper case because CONTINUOUS was a big deal then and it hat to be shouted loudly ;-)