RPN-25 CE is a simulation of Hewlett-Packard's popular second-generation scientific calculator HP-25C.

Released on August 1, 1975, the HP-25 scientific calculator was the second member of the so-called "Woodstock" series (between the HP-21 and the HP-22.) It was followed a year later by the improved version HP-25C which sported "continuous" (non-volatile) memory. Both versions were discontinued in 1978.

RPN-25 CE is a massively enhanced – yet fully compatible – version of the HP-25C.


Features

• Easier to use and much faster than the HP-25C


• Photo-realistic look


• Full compatibility with the HP-25C


• Programmable (up to 999 steps)


• Insert and delete program steps
  (with automatic address correction)


• Programmable text output right below the display


• Up to 15 programmable User Keys with key legends
  Tutorial (US), Tutorial (A4)


• Program Auto-Start option


• 100 symbolic labels


• 100 registers visible at a glance


• Unrestricted STO and RCL register arithmetic
  (incuding "double register" ∑+ and stack)


• Print program listing and description, or mail them as PDF documents


• Unlimited program library with filter for quick access


• More than 150 programs included


• Programs may contain comments


• 100 flags, all visible (F0..F9 optionally in display)


• More than 270 functions and operations not available on the HP-25


• Runs all functions of the HP-32E


• Runs a large number of HP-41 programs with little or no modification


• "Continuous" memory


• Thousands separators (optional)


• High-contrast display (optional)


• Key-click, key-glow, haptic feedback (all optional)


• Variable pause durations (up to a day)


• Swipe left across display to correct wrong number entries


• Swipe right across display to show the stack and Last X


• Display all registers in a single view (tap display once)


• Extended stack operations


• Cut/copy/paste display values and program steps


• Display and annotate programs


• Conditional program looping


• Save, Print, Share programs


• Battery warning indicator (all decimal points except the current one lighting up)


• Clock display (AM/PM or 24 hours – tap f or g, then the PRGM-RUN switch)


• Self-check: press STO ENTER. Tap any key to clear the display.


• Import and run programs created on the HP-25 simulator GO-25


• Import and run programs created on the HP-32 simulator RPN-32 CE

• Vintage Mode: closely simulate a real HP-25.
  Extended features of RPN-25 are not shown.


• Thousands Separators: if on, numbers larger than 999 will be shown with separators (comma or decimal point)


• Show Key Fronts: if enabled, tapping the g prefix key will reveal the hard-to-read functions printed on the key fronts.


• Flash Keys: if enabled, tapped keys are shortly highlighted. Useful if sound volume is very low or off.


• Show Prefix Indicators: if enabled, prefix keys like f, g, STO will be marked with a white outline as long as they are active. A prefix key may be tapped again to deactivate it.


• Auto-Select Step 00(0): if on, leaving PRGM mode will set the current step to 000, simplifying running the program by pressing R/S.


• Auto-Start on Prog Loading: a program saved with this setting on will automatically start running at step 1 after loading.


• Prog Steps: choose between 99 or 999 program steps. Note that traditional GTO instructions work only up to step 99. Use branches to symbolic labels for the full range.


• Pause Length: Set to 1, 2 or 5 seconds. To ignore PAUSE instructions, select 0. The instruction PSE LEN allows arbitrary pause lengths of up to a day.

• • New Feature
    The instruction "ERROR nn" with nn = 99 will cause the display to blink rapidly three times.

• • Bug Fix
    In the sample program 41-Curve Fitting (Kolb), the equation for curve 3 ("Combined Linear and Hyperbolic") was incorrectly shown
    as y = a + b/x + c/x instead of y = a + b•x + c/x. Tap "Restore Sample Progs" in the program list to see the change.

• • New Features
    – Toggle LED vs. High-Contrast display: f double-tap display
    – Toggle thousand separators on/off: f triple-tap display
    – Setting flag 41 causes ∑+ and ∑- to use the HP-41 locations of statistical registers.
    – The trig mode indicator DEG is switched off after the selected "Pause Length".
    – Added warning when attempting to alter a Sample Program.
    – The trig mode indicator DEG is switched off after the selected "Pause Length".
    – "FC?S nn" (renamed to "FC?S/C nn") acts as "FC?C nn" if flag 41 is set.

• • New Sample Programs
    – "Holidays multilingual" shows the date of Ash Wednesday, Easter, Ascension, Whitsun, and
        Corpus Christi for any year in the range 1583 to 4099 in three languages (English, Spanish, German).
    – "41-Curve Fitting (Kolb)" automatically finds the best fitting curve (out of 20) for a given set of data points.
        (Download the literature)

• • Changed Instruction
    –  ∑SWAP41 nn (was ∑SWAP41)
        Swaps the current RPN-25 statistics data block with the HP-41-compatible block at the location Rnn.

• • Bug Fixes
    – Calling up the Rydberg constant in the sample program CODATA 2018• would cause a crash.
    – Alignment of messages (MSG,MSGP,MSGP) could be incorrect in some cases.
    – In the program listing, 4-digit literals could show up with an unwanted centered 0.
  

• • Improved Statistics Functions
    New and changed instructions can handle up to 13 statistics data blocks of 7 registers each in parallel.

• • Bug Fix
    This version fixes buttons Import and Delete not being enabled by selecting a program.
  

• • Internal optimizations and cleanups
    New sample programs are now automatically loaded when opening the list of programs.
    Changed the default font for program listings from Courier New to Menlo.


• • Modified the info screen to avoid clipping by the Dynamic Island.
  

• • Enhanced Support of Extra Functions
    Tap "Details" to directly access descriptions and examples in Safari
  

• • Improved math functions GCD and LCM
    Both functions can now have up to 4 arguments
  

• • Vintage Mode:
    – No RCL register arithmetic
    – No dotted register names, e.g. "R.5"
    – No access to registers R8 and R9
    – Program execution speed comparable to real HP-25
    – The vintage mode setting is stored along with the program

• • Bug Fixes:
    – Instructions GET SEPS and HAPTICS? now work correctly in interactive mode.
    – Executing CLOCK when the clock was already running would not clear the AM/PM indicator.

• • Trigonometric mode indicators:
    DEG, RAD, and GRD indicators are never shown in vintage mode.
    In normal mode, the default setting DEG appears only on the high-contrast display.
  

• • Vintage Mode:
    Controlling vintage mode via "magic numbers" 19390104 and 19390105 has been removed.
  

• • Bug Fix: In some situations, pressing the R/S key would alter the stack.
  

• • Vintage Mode:
    Vintage Mode may now be turned on or off in Settings.
    Features not available on the HP-25 are not presented anymore.
    Controlling vintage mode via magic numbers 1939010x has been removed.
  

• • SST and BST in RUN mode:
    - SST shows the current instruction as long as the key is depressed, then executes it.
    - BST shows the previous instruction as long as the key is depressed, then makes the step current.
    Both actions may be cancelled by dragging the finger off the key.

• Improvements:
• • The DOW (day-of-week) function does not require the display format to be set to FIX 6 anymore.
  
• • Decimal point and thousands separator symbols are now set according to the locale.
• • Power switch: drag left or double-tap to turn calculator off. Drag right, tap, or double-tap to turn calculator on.

• • High-contrast display:
    The real-time clock also shows the date and the weekday
    (f PRGM-RUN: 12-hr with AM/PM, g PRGM-RUN: 24-hr)
  

• • New instructions:
    - HAPTIC f sets the haptic level of the iPhone to level f (1…3, 0 for no haptics)
    - HAPTIC? returns the current haptic level (0…3)
  

• Bug Fix:
• • Issues with DOW (day-of-week) function. Now works correctly for all Gregorian dates (Oct 15, 1582 and later.)

• • High-contrast display:
    - The mantissa of a number (g MANT) is now shown without thousands separators.
    - The DOW (day-of-the-week) function shows the date as text, in addition to the day number.
  

• • Pressing a User Key now clears any user message, just like pressing a regular key does.


• • Numeric values shown in MSG, MSGP, MSGS instructions may now be forced to show in FIX 0 format
    (by prefixing their name with "I" [capital-i]).


• • Added stack indirection (by prefixing stack register name with "i") when specifying values to show in MSG, MSGP, MSGS instructions.

• • New instructions:
    - BASE? b (b = 2…9) tests if the positive integer part of X represents a valid number in base b.
    - FLOOR rounds down towards negative infinity.
    - CEIL rounds up towards positive infinity.
    - CF0to9 clears flags F0 to F9.
    - SHOW41, HIDE41 control the visibility of the flag 41 indicator..
    - Convert between units of power (kW, mechanical horsepower hp, metric horsepower PS).

• • New sample programs:
  
    - CODATA 2018•  WATCH DEMO
      Easy access to 354 named physical constants. Use it as a template for your own lookup tables.
  
    - Boolean Functions and Base Conversions•
      AND / OR / XOR / NOT operations and conversions from any base to any other (base = 2…10).
  
    - Mixing•
      Mix cold and hot liquids to obtain a specific amount of liquid at a specific intermediate temperature.

• Bug Fixes:
• • Copy/paste in PRGM mode didn't work if high-contrast mode was turned on.
• • Fixed issues with wrapping/unwrapping number literals followed by a CHS instruction.
• • The sequence of digits defining a number with an exponent that is a multiple of 10 did not translate correctly into a literal.

• • High-contrast display
    - Switch between the traditional LED display and an easy-to-read LCD-like display
    - Triple-tap display or use HC DSP to switch on and off
  

• • New or changed instructions:
    - HC DSP turns off high-contrast display if x = 0, otherwise turns it on.
    - GET SEPS returns the thousands separators setting: 0 = OFF, 1 = ON
    - SET SEPS sets the thousands separators setting: 0 = OFF, other = ON.
    - SPEC DSP shows special pattern for x = 1…4 (LED display), or x = 1…25 (LCD display).
    - CLOCK sets the appearance of the real-time clock. x = 1: 12-hr am/pm, 2: 24-hr, other: no clock
    - DATE shows the clear-text weekday and date if high-contrast display is on.
  
  The indirection character for showing register contents in MSG, MSGP, MSGS messages has been changed from "-" to "i".

• • Quick Access to LBL and GTO / GSB
    - Tap the LG button in the program list view to quickly see all labels in your program.
    - Double-tap LG to see all branches to labels.
    - Sort by step or item.
    - Double-tap a label or branch to select the corresponding program step.

• • User Keys may now have leading blanks.


• • Suppress Auto-Start of a program by setting flag 99 before importing.

• • New instructions:
    - BACK s jumps back s program steps.
    - DEL Y removes y, drops stack down
    - DEL Z removes z, copies t to z
    - Y→ZT copies y to Z and T
    - Y→T copies y to T
    - Z→T copies z to T
    - PRGM stops program and switches to PRGM mode
  

• • Sample programs:
    (NOTE: Programs featuring User Keys are identified by a trailing dot (•).)
    - 41-Terrestrial Geodetic Distance•
    - 41-Giant Planets 2022•
    - NPV & IRR• (for up to 92 cash flows)
    - Solve for f/x)=0 Newton• (now with User Keys)

• Bug Fixes:
• • Stopped instruction name from appearing below display when it shouldn't.
• • Fixed display issues when running on iPod touch.
• • Fixed instruction name SPEC VIS showing as SPEC DSP.

• New:
• • New instructions:
    - P→S copies primary registers R0..R9 to secondary registers R.0..R.9
    - SHOW STK and HIDE STK control the appearance of the stack in the display
    - SPEC DSP produces special displays (all blanks, all "-", all "o")
    - STEP VIS controls the appearance of the program step indicator below the display
    - FLAG VIS controls the appearance of flag indicators 0 to 9 in the display
  

• • Sample programs:
    (NOTE: Programs featuring User Keys are identified by a trailing dot (•).)
    - _Demo 25• (showcases advanced features of RPN-25)
    - Cost and Price Computations•
    - 41-Sudoku Solver
    - 41-Sudoku Puzzles
    - 41-Discriminant of a Polynomial•
    - 41-Palindromic Polynomials•
    - 41-Garden-Hose Method•

• Bug Fixes:
• • User Keys were not responsive while the display showed the stack.
• • On loading an auto-start program, a command string could show up below the display in certain situations.
• • In the program listing, wrapping a multi-step number like .005 into a single step would drop the mantissa.
• • Program comment lines would behave oddly in some situations.

• New:
• • User Keys
    - Five keys, positioned directly above the display
    - Up to 15 keys when using f and g modifiers
    - Each key may have a legend (1 to 6 characters)
    - Unnamed keys, or keys named with a single underscore, are ignored
    - The legend and the operation associated with each key may be changed anytime, even by a running program
    - Direct and indirect subroutine calls
      Tutorial (US), Tutorial (A4)


• • Auto-Start
    - A program saved with the setting Auto-Start turned on will automatically run from step 1 after loading.
  

• Bug Fixes:
• • Suppressed illegal key pairs in program mode: STO/RCL/GTO followed by EEX or R/S.
• • Program step display is now turned off if power is off.
• • If turned off, the program step display will not reappear on switching from PRGM mode to RUN mode.
• • Pasting a program larger than 100 steps into the display in 99-step mode would cause a crash.

• New:
• • Data files:
    - Create, load and modify files that contain register data only (R00..R99.)
    - Run a program with different pre-recorded sets of register data.
  
• • New sample program:
    - "41-Travelling Salesman" (demonstrates the data file feature)

• New:
• • New instructions:
    - Functions LambertW and LambertV
    - STO YZT and RCL YZT: store and recall stack registers Y, Z, and T without affecting X
    - Comparisons: x≈y and x≈0 ("almost equal"). Execute next step if x is closer to y or 0 than 2E-9, otherwise skip next step.
    - CLRX. Executes CLX without disabling automatic stack lift.
• • New sample programs:
    - "Interest Amount & PMT"
    - "Discrete Fourier Transform"

• Bug Fix:
• • Pasting a text listing, e.g. from Mail, into the display would fail on certain instructions.

• New:
• • Julian Day Number (JDN) accepts a time value in Y.
    Illegal date and time values are replaced by current values.
• • In vintage mode, NOP instructions as targets of branches are not automatically converted into LBL instructions.

• Bug Fix:
• • Inserting a MSG operation would cause a crash

• New:
• • Symbolic labels (00..99), not associated with step numbers.


• • Selectable program memory size (99 or 999 steps)


• • Single-step constants ("number literals")


• • Indirect branching via stack or regular registers
  


• • User messages ("texts")
    - MSG text puts the message text right below the display.
    - MSGP text puts the message text right below the display, then executes PAUSE.
    - MSGS text puts the message text right below the display, then stops program execution.
      text may be any text of up to 30 characters, left- or right-aligned or centered.


• • Program comments ("texts")
    - // text
     Show free text in any step of the program listing.


• • New instructions:
    - SKIP n skips 0 to 9 program steps
    - END stops program execution without returning to step 0
    - JDN returns the Julian day number of a date
    - DY2000 returns the number of days between a date and Jan 1, 2000
    - SND nn plays sound nn (00..99)
    - NUM2DIGS nn decomposes the 10-digit mantissa and stores the digits at Rnn..Rnn+9
  - DIGS2NUM nn creates number from the 10 digits stored in Rnn..Rnn+9
  - ROUND n rounds x to n fractional digits
  - DELAY works like PAUSE but without the "PAUSE" message
  - ISGi nn, DSEi nn: indirect versions of ISG nn and DSE nn
  - SFi N, CFi N, FS?i N: handle flags indirectly via any stack register
  - ST41, RC41: store and recall flag 41
  - x³ returns the cube of x
  - y^x{0} is the same as y^x, except that 0⁰ = 1


• • Instructions INCR and DECR have been renamed to x+1 and x–1.


• • Long-press the step number to show or hide the last executed step


• • Entering a numeric value while pausing restarts the pause with each keypress.


• • Overflow on ∑+ and ∑- is now handled like on a real HP-25.
  Setting flag 41 simulates the HP-41's behavior where
  register overflow does not trigger a program error.


• • Flags 0…3 and 41 are shown on the display if set (F3 only if F41 is set.)


• • Refined behavior of RTN instruction: in a running program, if no return address is available, program execution is halted. In interactive mode, step 0 is selected, as before.


• • To turn the calculator off, swipe the power button left. Simply tapping it doesn't suffice anymore.


• • Sample programs (most of them using symbolic labels):
    - "41-Conics"
    - "41-Stirling Numbers"
    - "41-Stirling Numbers generalized"
    - "41-Ramanujan Tau Numbers"
    - "41-Multinomial Coefficients"
    - "41-Fibonacci, Tri-, Tetra, k-nacci"
    - "41-Fibonacci Multiprecision"
    - "41-Apéry's Numbers"
    - "41-Cyclic Universe 1a"
    - "41-Cyclic Universe 1b"
    - "41-Gauss-Legendre 4-point"
    - "41-Diff. Equations 2nd Order"
    - "41-Weierstrass-Durand-Kerner"
    - "41-Norm of a Matrix"
    - "41-Integral over a Sphere"
    - "41-Arc Length of Parametric Curve"
    - "41-Delta T (∆T)" (343 steps)
    - "41-Giant Planets 2021"
    - "41-Debye Function"
    - "41-Multiple Series"
    - "41-Successive Approximation"
    - "41-Euler Transformation"
    - "41-Illuminated Fraction of Moon"
    - "41-NumInt - Double Exponential" (347 steps)
    - "41-Euler-Lagrange Equation" (347 steps)
    - "41-Downhill Simplex Method" (465 steps)
    - "41-Bulirsch-Stoer Method" (541 steps)
    - "41-Vector Calculus Curl, Div, Grad, Lapl" (627 steps)
    - "41-Polynomials" (646 steps)
    - "41-Anchorage Knik Arm" (861 steps)
    - "41-Equilateral Triangle Puzzle"
    - "TVM - Time Value of Money"
    - "Dial"

• Bug Fixes:
• • TIME did not lift the stack
• • GTO 78 would incorrectly show as GTOc_COS

• New:


• • Execute Extra Functions in RUN mode
• • Changed: double-tap display for Extra Functions; triple-tap for Settings


• • VIEW instruction to watch any memory or stack register while program is running
• • CLD (Clear Display) restores normal display after VIEW
• • DSMSTO and DSMRCL (Display Mode Store and Recall) store or restore display settings


• • REGSET sets any range of registers to a given value
• • REGSORT sorts any range of registers
• • xi≷yi: swap registers defined in X and Y


• • Date instructions:
    DATE: current date (month, day, year)
    DATE+: add number of days in X to the date in Y
    ∆DAYS: number of days between the dates in X and Y
    DOW: day of the week, day number, week number
    MDY➞YMD, YMD➞DMY, DMY➞MDY, etc.: date format conversions


• • 100 flags (up from 10), with states visible in extended register view.


• • Additional flag instructions:
    FC? nn: tests if flag nn is cleared
    FC?S nn: tests if flag nn is cleared, then sets it
    FS?C nn: tests if flag nn is set, then clears it
    TOGF nn: toggle flag nn


• • F? renamed to FS?
• • Flags 24 and 25 for error handling
• • Flag 41 for HP-41 compatibility
• • STFLAGS, RCFLAGS to store/recall groups of 32 flags
• • CFInd, SFInd clear/set indirection mode for flags


• • Additional comparison instructions:
    x<NN, x≤NN, x=NN, x≠NN, x≥NN, x>NN: compares x with Rnn defined in Y
    x<nn, x=nn, x>nn: compares x with Rnn


• • FILL RAN# now accepts a user-defined range


• • Mathematical and physical constants (CODATA 2018-compliant)
• • No change of program counter when ISG/DSE is executed on the keyboard
• • Indirect register addressing ignores sign and fractional part of the argument
• • In vintage mode, ISG, DSE, RND, RAND, and CLEAR ∑ are not shown and dont' work.


• • Sample programs:
    - "41-Extrema"
    - "41-Parabolic Interpolation"
    - "41-Infinite Nested Radicals"
    - "41-Large Factorials"
    - "41-Multi- and Hyperfactorials"
    - "41-Factorial Digits"
    - "41-Kaprekar Series"
    - "41-Golomb Sequence"
    - "41-Euler Numbers 1"
    - "41-Euler Numbers 2"
    - "41-Harmonic Numbers"
    - "41-Pell's Equation"
    - "41-Kepler's Equation"
    - "41-Easter Date"
    - "41-Equilateral Triangle Puzzle"
    - "41-Multivariate Gamma, Digamma"
    - "41-Loxodromics"
    - "41-Geodesic Distance"
    - "41-Square Root modulo m"
    - "41-Unrestricted Partitions"
    - "41-Permutations"
    - "Dial"
    - "Amortization" (update)
    - "TVM – Time Value of Money" (update)

• Bug Fixes:
• • ISG/DSE commands were susceptible to internal rounding effects
• • Deleting a block of steps could result in wrong branch targets

• New:


• • 100 registers (up from 20)


• • New register view showing all 100 registers


• • Print program listing or program description, or email them as PDF file


• • Store/recall arithmetic between X and any stack register


• • Define register arguments directly in the Extra Functions list


• • New Extra Functions:
    STO<op>nn, RCL<op>nn: direct register arithmetic between x and register nn (0..99)
    STi<op>nn, RCi<op>nn: indirect register arithmetic between x and register nn (0..99)
    xi≷ nn: swap x with register defined in register nn (0..99)
    STO<op>N, RCL<op>N: direct stack arithmetic between x and stack register N
    STi<op>N, RCi<op>N: register arithmetic between x and register nn (0..99) defined in stack register N
    x≷ N: swap x with any stack register N
    xi≷ N: swap x with any register nn (0..99) defined in stack register N
    x<Rnn, x=Rnn, x>Rnn: compare x with any register nn (0..99)
    ISG nn, DSE nn: increment/decrement register nn (0..99) and skip if condition met
    ISG N, DSE N: increment/decrement stack register N and skip if condition met
    ISGi N, DSEi N: increment/decrement register nn (0..99) defined in stack register N and skip if condition met
    SND nn: play sound defined by value (0..99) in register nn (0..99)
    CLR ALL: clear all registers (R00..R99)
    CLR EXT: clear all extended registers (R20..R99)
    CLRGX: clear a block of registers with optional skipping
    REGCOPY: copy a block of registers
    REGSWAP: swap two blocks of registers
    REGS ALL: show all registers (R00..R99)
    SIGN: return -1, 0, or +1 if x is negative, positive, or zero
    PRIME?: set flag 0 if x is a prime number (x ≤ 4,294,967,295)
    ERF/ERFC: Gauss error function and complementary error function
    Bernoulli: returns xth Bernoulli number
    BesselJ: Bessel function of the 1st kind of order y of x
    BesselY: Bessel function of the 2nd kind of order y of x
  Zeta: return the Riemann zeta function ζ(x)
  ERROR nn: replaces the previous functions ERROR 1 and ERROR 2


• • Optional vintage features
    Send 19390104 to register 0 to toggle some features on and off:
    - New program step replaces the next step instead of being inserted
    - ISG, RND and CLEAR ∑ labels are hidden (but still functional)


• • A program running longer than one minute will emit a short beep when executing the final GTO 00 command


• • Tap f or g, then the PRGM/RUN switch to see a 12- or 24-hour clock


• • Improved accuracy in extreme cases of y^x with positive, integer x.
    For example: 1.0000001^2²⁷ = 674530.4707, not 674530.4760


• • Double-tapping "Continuous Memory" doesn't show the Info screen anymore.
    Use the info button instead.


• • Call up "What's New" anytime from the Info screen


• • New sample programs:
    - "Amortization"
    - "Bell Numbers Advanced"
    - "Decimals of e"
    - "Decimals of Pi"
    - "Multi Curve Fitting"
    - "NPV and IRR"
    - "Square Roots & Integer Power
    - "TVM – Time Value of Money"

• Bug Fixes:
• • Fixed display issues when using the iPhone in "Zoomed" mode
• • The RND function didn't work correctly in regions using a comma as decimal point
• • Double- or triple-tapping the empty program listing could cause a crash
• • Setting the haptic feedback level didn't check sufficiently for the correct code
• • CLR ALL from RPN-32 was translated incorrectly
• • Compatibility with iPhone 12

• New:
• • More than 80 new functions added
• • Much simplified inserting of Extra Functions:
    1. Triple-tap display in PRGM mode
    2. Double-tap desired function

• Bug Fix:
• • The thousand's separator setting was lost after restarting the app

• First public version.

RPN-25 CE