9 ms·

You need "2 <ENTER> 3 +" to add two and three. Your "3 <ENTER> +" is adding 3 and 3.

by breuwi 4y ago

quanticle 4y ago
Thanks for clarifying. I didn't realize that the input buffer was separate from the stack.
- inejge 4y ago
  For the classic HP RPN, it isn't. Numbers are entered directly into the X register. ENTER does several things: it finishes the input, copies the new value in X to Y (shifting the rest up) and inhibits "stack lift", so the stack won't be automatically shifted up when you start entering the next number. Sounds complicated, but in practice you don't think about it at all.
  - chungy 4y ago
    Later calculators (the HP 42 and 48 lines) would basically accommodate either mode of operation. You can perform a calculation immediately without pressing ENTER to put it on the stack, or you could put it on the stack with ENTER first and it'll still do the same thing when you press an operator key. I use an HP 48G+ frequently and I pretty much do both styles without any obvious rhyme or reason from my viewpoint. I just sometimes do one or the other.
    - Pinus 4y ago
      I think you mean 28, not 42 — the 42 is also "classic" 4-register RPN. And I’m writing this mostly to push for the excellent Free42 emulator, which runs on just about everything (Windows, macOS, Linux, Android, iOS), and also powers the DM42 hardware emulator mentioned above. Only problem with it is that emulated buttons on a touchscreen are nothing like the real thing; I keep missing keystrokes.
      - trasz3 4y ago
        [dead]
      - jaclaz 4y ago
        I can confirm, the 28C actually shows the 4 (viewable) registries of the stack, numbered on the left as: 4: 3: 2: 1: So, if you input 4 [ENTER], 3 [ENTER], 2 [ENTER], 1 [ENTER] you have: 4:4 3:3 2:2 1:1 But if you input 4 [ENTER], 3 [ENTER], 2 [ENTER], 1 you have: 3:4 2:3 1:2 1 if you then press +, you get 3 in both cases, which is the sum of the bottom two lines in the display. Those are either the same as the "old" x and y registers or the sum of last input and the bottom register, same as the old x.
      - chungy 4y ago
        Yes you are right, I did mean that :)
- ilyt 4y ago
  It's easier to get how they work on calculator or emulator that shows bigger part of the stack

You need "2 <ENTER> 3 +" to add two and three. Your "3 <ENTER> +" is adding 3 and 3.

by breuwi 4y ago

You need "2 <ENTER> 3 +" to add two and three. Your "3 <ENTER> +" is adding 3 and 3.

quanticle 4y ago

Thanks for clarifying. I didn't realize that the input buffer was separate from the stack.

inejge 4y ago
For the classic HP RPN, it isn't. Numbers are entered directly into the X register. ENTER does several things: it finishes the input, copies the new value in X to Y (shifting the rest up) and inhibits "stack lift", so the stack won't be automatically shifted up when you start entering the next number. Sounds complicated, but in practice you don't think about it at all.
- chungy 4y ago
  Later calculators (the HP 42 and 48 lines) would basically accommodate either mode of operation. You can perform a calculation immediately without pressing ENTER to put it on the stack, or you could put it on the stack with ENTER first and it'll still do the same thing when you press an operator key. I use an HP 48G+ frequently and I pretty much do both styles without any obvious rhyme or reason from my viewpoint. I just sometimes do one or the other.
  - Pinus 4y ago
    I think you mean 28, not 42 — the 42 is also "classic" 4-register RPN. And I’m writing this mostly to push for the excellent Free42 emulator, which runs on just about everything (Windows, macOS, Linux, Android, iOS), and also powers the DM42 hardware emulator mentioned above. Only problem with it is that emulated buttons on a touchscreen are nothing like the real thing; I keep missing keystrokes.
    - trasz3 4y ago
      [dead]
    - jaclaz 4y ago
      I can confirm, the 28C actually shows the 4 (viewable) registries of the stack, numbered on the left as: 4: 3: 2: 1: So, if you input 4 [ENTER], 3 [ENTER], 2 [ENTER], 1 [ENTER] you have: 4:4 3:3 2:2 1:1 But if you input 4 [ENTER], 3 [ENTER], 2 [ENTER], 1 you have: 3:4 2:3 1:2 1 if you then press +, you get 3 in both cases, which is the sum of the bottom two lines in the display. Those are either the same as the "old" x and y registers or the sum of last input and the bottom register, same as the old x.
    - chungy 4y ago
      Yes you are right, I did mean that :)
ilyt 4y ago
It's easier to get how they work on calculator or emulator that shows bigger part of the stack