RPN-45 SD 4+

Very nicely done HP-45 emulator, plus the "extra" features are a nice bonus. Beautifully executed, including the timer mode. I have other calculator emulators with simulated 7 segment LED displays, but none that capture the look of a real vintage 70's display nearly as well as this one. One minor criticism: the shifted key labels are a bit hard to read on an iPod (standard display). Overall an excellent addition to my HP calculator "virtual" collection, and compared to what I've paid for some of them, this one is a real bargain.

Fun to have a replica of this machine that I first learned on 45 years ago.

Kind of fun to have the enhancements too, although these do stop short of current high-end apps. The best part, just as a way for any such app to extend the functionality of the keyboard, is actually the double-mode shift key, which gets you yellow functions on the first push and then red functions on the second push, before cycling back to neutral. Shows you how little you depend on having the shift key toggle back to neutral on the very next push: pretty rarely. One more push won’t hurt you.

ENGineering display mode is something I use a lot, a nice update to have, and also the HYPerbolics button. And the additional STO/RCL registers are welcome. And the regression and estimate keys, and permutations/combinations, could come in handy, though I haven’t tried them yet, And the quadratic/cubic solver.

The complex numbers are a nice addition too, similar to the 15c treatment although with some different special-function keys.

The simultaneous equation solvers are ok too, I suppose, though as matrix math they’re kind of a one-trick pony compared to the 15c’s treatment (Vicinno for instance) which will handle five matrices of any shape, not just three that are one square and two column vectors — and will let you perform any operation you like with them, not just solve simultaneous equations.

So except for the nostalgia trip, my first choice for a capable two-shift-button machine with quickly accessible functions is actually the 15c. (Which also is programmable.)

Or if you really want a workhorse-machine app you should get Thomas Okken’s Free42 — an open-source rewrite of the HP42s — which has a lot more functions and shows two stack levels and both halves of a complex number, so it’s way easier to keep track of what you’re doing, And lets you write alphanumeric labels for programs, variables, matrices, etc. But does pay for having so much power by having many of the functions somewhat buried in menus, not as quick to reach as on the 45 or the 15c,

But I do enjoy having the 45 around, and it does do way more than you’d ever expect a 45 replica to do.

I've been using a real HP-45 since 1973. Willy Kunz has done an excellent job recreating and then extending the versatility of the real thing in this simulation. I love it! My only gripe is that the gold and pink fonts he used for the extended functions aren't as readable on an iPhone 6 as the gold font he used for the standard functions. Very minor, and easily correctable.