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Thomas Okken · 02-10-2020, 08:29 PM

(02-10-2020 03:49 PM)Joe Horn Wrote: Strangely, RCL Σ+ doesn't push its values onto the stack the same way on all models. Some directly overwrite X and Y, leaving the previous values of Z and T in place (e.g. the HP-55, 67, and 29), while others first lift the previous values of X and Y into Z and T (e.g. the HP-45, 33E and 34C).

Did RCL Σ+ disable stack lift on any models? That would seem like a crazy thing to do, but I seem to recall that some model did so, which tells me that it must be true, because "The curse of aging is a sort of creeping infallibility."

On the machines I'm familiar with, RCL Σ+ (a.k.a. SUM on the HP-42S) overwrite X and Y and don't lift the stack. I think the idea was to match the behavior of MEAN and SDEV.