HP-27s and direct solutions legend

[Dave Britten]

I also often sing the praises of the 27S. I really wish HP had made a 27SII with RPN. The solver is really powerful, and it'll even do symbolic solutions using functions like HR() and HMS(), so you can enter an equation like "HR(T2)-HR(T1)=HR(TD)" for calculating the difference between two times in H.MMSS format, or calculating a time +/- some span of time. I've also got mine stuffed full of a bunch of different probability distributions and formulas, and the SPFV/SPPV/USFV/USPV functions make it easy to do highly accurate and sophisticated financial calculations.

I'd love to see Free42 forked into Free47, maintaining all the existing 42S features, but also including those that are specific to the 27S, like the financial functions, list editor (which makes a great, if simplistic account register), and symbolic solver. For now, I've implemented most of the financial features as keystroke programs, and the DM42 is fast enough that solving RPN programs is plenty quick compared to the HP symbolic solver (though it's still often easier to enter and read a quick symbolic formula compared to a keystroke program).