history of the 4-level stack

[axd1967]

Quote:Even though the Friden EC-130, circa 1964, and the Monroe Epic Calculator, circa 1966, do not mention "RPN" or Lukasiewicz (roughly pronounced woo-ka-shea-vich), they clearly operated according to a postfix, parentheses-free, 'RPN'-like fashion - and they each had a 4-level push-down stack. Undoubtedly, HP improved on this with the repeating T register and seems to be the first company to use the term RPN (which they patented).

Interesting, this suggests that '4' is an interesting value.

Quote:I think if you search the archives you will many discussions about RPN stack levels and I would say Jose Mesquita provided a good summary in his response - that it is all about compromise. Less than 4 levels is undesirable (a 2 level stack would be the absolute minimum to even qualify as a calculator) and more than 4 level stacks would make memorization of stack contents difficult for most people.

Machine searched all archives (1,2,3,4) for "Jose Mesquita" but found nothing, sorry. Can you provide links to the relevant article(s)?

BTW, not sure '4' is an optimal value, see The Magical Number Seven, Plus or Minus Two (although '4' also pops up in the article), which dates from 1956, so HP might have been aware of it.

Meanwhile, I had already found this thread most interesting.