RPN-45 — The first photorealistic HP-45 simulator for iOS devices

Version 4.1

RPN-45 is a photorealistic simulation of Hewlett-Packard's second scientific hand-held calculator from 1973. Made exclusively for iOS devices (iPad, iPhone, iPod touch).

It comes in several versions: RPN-45 HD for the iPad, RPN-45 SD ("Small Display") for iPhone and iPod touch.
The original HP-45 without extensions (apart from additional optional conversions) is available as Vintage-45.

The touchscreen technology of iOS devices, the animated keys with click sound, the larger-than-life view of the HP-45 (on the iPad), all blend into an experience that comes as close to using the real thing as any simulation possibly can.

The simulation includes all functions the HP-45 ever had, including the hidden timer. Processing times have been carefully measured and reproduced on RPN-45. Of course, thanks to modern computer technology, the simulation performs calculations with much greater accuracy than the HP-45 ever did.


    On RPN-45 HD only:

Discover many more features in the New sections of the Version History below.



Version History RPN-45

4.1 – Jan 11, 2019
  • • Print commands now work like on the iPhone version. You can print the display value, the stack, the registers, or a blank line - even rip off the paper tape - directly from the keyboard after tapping the gold key once or twice. Multiple blank lines are created automatically by holding the key down.
  • • Printing the display value while entering a number always prints in grey color
  • • Roll-up stack: tap gold key twice, then tap Roll-down
  • • Statistics register names (shown by long-pressing the register window) are suppressed in timer mode and complex number mode
  • (RPN-45 SD) Optional haptic feedback on key presses, if supported by device and iOS version (see settings)

4.0 – Sep 14, 2018
  • • Send register values to another device running RPN-45:
      1. Print registers on paper tape (gold-gold-REG)
      2. E-mail the tape
      3. Copy the mail text and paste into display

  • • Save and restore registers:
      1. Print registers on paper tape (gold-gold-REG)
      2. Long-press any register line on paper tape and drag to the display

  • • Import register values from other sources:
      1. Create one value per line, each followed by the desired register number (0..19)
      2. Copy desired lines, then paste into display

3.9 – Aug 17, 2018
  • • Extended paper tape sharing (AirDrop, Notes, Dropbox, and more)
  • • Paper tape can be set to bold printing (press the printer's TXT button to see the option)

3.8 – Apr 16, 2018
  • • Separate backup area for all registers:
      – STO R↓ = copy registers to backup area
      – RCL R↓ = retrieve registers from backup area
      – STO x≷y R↓ = swap registers with backup area
  • • To clear the stack and all registers, tap the gold key twice and execute CLx
  • • In print mode ALL, all solutions of the linear equation solver are shown on the tape
  • • When computing integral roots of a complex number, e.g. (3+5i)1/6, multiple results are returned in X and the registers (up to 10).
  • • For statistical calculations, ∑y², ∑xy, ∑x²y are now available in registers R16, R17, R18
  • • STO x≷y ∑+ swaps statistics registers R5..R8 with extended registers R.5..R.8
  • • Register view reveals the names of the statistical registers (long-press on RPN-45 HD)
  • • Improved pasting of values into display, e.g. by dragging from paper tape
  • • Changed input order of weighted mean arguments: x = value, y = weight (frequency)

3.7.1 – Jan 4, 2018
  • • Added logy function (logarithm of x to base y). Even for complex numbers.
  • • Improved trig functions for extremely small angles
  • • Printing stack in complex mode shows imaginary part
  • • All solutions of quadratic or cubic equations are shown on the printer
  • • Printed time values may be copied and pasted into display
  • • Added green ribbon to paper tape printer
  • • Corrections in built-in manual

    Bug Fix:
  • • On restarting RPN-45 in complex mode, the stack was not restored correctly

3.6 – Feb 28, 2017
  • • Better FRAC results for large arguments

    Bug Fix:
  • • RND didn't round correctly certain values in SCI and ENG mode

3.5 – Oct 2, 2016
  • • Easter date for 1583 thru 4099: set y = 0, x = year, execute DATE
  • • Improved keyclicks
  • • Calculator sounds mix with background audio and have their own volume control

    Bug Fix:
  • • Copy/pasting of time values in timer mode

3.4 – July 28, 2016
  • • Long-press a line on the paper tape to copy it to the pasteboard
  • • Long-press and drag a line from the paper tape to the display to paste it
  • • Improved results for SIN, COS, TAN with very large arguments
  • • Decimal addition/subtraction for higher precision

3.3 – May 20, 2016
  • • Localized number grouping (toggle with "FIX .")
  • • Improved display (contrast, digits)

    Bug Fixes:
  • • Large arguments of tanh(x), i.e. ≥ 710, don't produce error message anymore
  • • Display issue when toggling group separators while entering number

3.2 – Feb 13, 2016
  • • Probability function also returns Inverse Cumulative Normal Distribution (in stack Z)
  • • Documented turning thousand's separators on/off in Info screen (tap "FIX .") HD version only

    Bug Fix:
  • • If no mail app active, no warning appears until trying to e-mail. HD version only

3.1 – Sep 2, 2015
  • • Thousand's separators (tap "FIX." to toggle on and off)
  • • Date display uses decimal point in all regions
  • • Battery warning printed in printer mode ALL
  • • If audio is playing on start-up, RPN-45 will not produce any sounds

    Bug Fixes:
  • • Fixed display format issue in FIX mode on 32-bit devices
  • • Negative date difference is shown correctly
  • • Changing settings while calculator is off doesn't turn on display
  • • In printer mode ALL, some operations would not print the result

3.0 – April 23, 2015
  • Paper Tape Printer
      - Use your HP-45 like an HP-91
      - Add annotations effortlessly
      - E-mail or print the tape
      - Select the ribbon color (black or blue)
      - Optionally print negative results in red
      - Three printing modes: MAN / ALL / NORM
  • Chess clock
      - Set game time limit
      - Show playing time of both opponents simultaneously
      - Interrupt and continue game any time
      - Audible and visual alert when game time is up
      - See number of moves played
      - Log game on paper tape
  • Last Stack operation
      - Restores the entire stack after an operation
  • • Convert integer part of display value to hexadecimal
  • Percentage of total function
      - Shows display value as percentage of sum created by the summation key
  • • Added solver for linear equations in 3 unknowns
  • • RCL register operations work with LAST x value (enter RCL 0 etc.)
  • • Print stack and print registers functions
  • • The cubic equation solver returns the type of the roots
  • • Regional angepasster Dezimalpunkt
  • • Localized decimal point
  • • Timer values show colons

2.5 – Feb 15, 2015
  • • HP-45 low-battery warning (all decimal points lit) if iPad's battery drops below 5%
  • • Polar-rectangular (and vice versa) conversion extended to hyperbolic mode
  • • Improved sound volume control
  • • Better legibility of extra functions
  • • 64-bit support

    Bug Fixes:
  • • Calculator didn't turn itself on automatically (iOS 8)
  • • Fixed display rounding error
  • • LastX didn't work if RCL / n produced an error

2.4 – Aug 23, 2014
  • • In SCI and ENG notation, command RND now rounds the mantissa only, not the entire number

2.3 – Mar 28, 2014
  • • Now with 30 backgrounds to choose from, PLUS import your own background image
  • • Improved y^x function, e.g. (-9)^4 will not produce complex result anymore
  • • In FIX display mode, no automatic switching to SCI mode anymore, unless required by number value [Super-45 only]

2.2 – Sep 18, 2013
  • • Improved INT and FRAC functions
  • • Full-screen display
  • • Compatible with iOS 7

    Bug Fixes:
  • • Register arithmetic now handles under- and overflow correctly
  • • Fixed pasting values dropping decimal point in certain regions
  • • Fixed typo in built-in instructions

2.1 – Oct 2, 2012
  • • Added ENG (engineering) display format
  • • Stack registers and calculator mode (normal/complex) are non-volatile
  • • Compatible with iOS 6

    Bug Fixes:
  • • Format of copied value if FIX 0 in effect
  • • ∆DYS: Incorrect number of days when second date was entered partially
  • • Wrong header language on page 3 of Super-45 instructions
  • • Crash when presetting the timer with an integer
  • • ➞P key would not animate in complex mode

2.0.1 – July 18, 2012
    - Estimates for Linear Regression
    - Weighted mean
    - Permutation
    - Combination (binomial coefficient)
    - Extended date calculations
    - Rounding of display value
    - Swap regular and extended registers, single or all at once:
      • STO x≷y n = swap register n with extended register n (1..9)
      • STO x≷y 0 = swap all registers with extended registers
  • • Landscape display mode with live registers and a life-size HP-45
  • • Improved keyboard response
  • • In Super-45 mode, mean and standard deviation are calculated for both x and y.
  • • Using the I key, it is now possible to enter four complex values on the stack.
  • • Selectable keyclick volume (off/soft/loud)

    Bug Fixes:
  • • Number entry is not terminated by calling up the settings screen
  • • Opening the settings screen before the calculator has turned itself on does not lock up the app
  • • No more automatic stacklift after Σ+ und Σ-
  • • Sign of complex arcsin and arccos functions
  • • A Julian date is correctly treated as negative value in calculations
  • • Tapping a key while a calculation is running doesn't clear mode "complex" anymore
  • • Stack wasn't cleared except in Super-45 mode
  • • Turning on "Non-volatile DP Setting" for the very first time could result in FIX 0 being set

1.4.6 – May 18/19, 2012
    New Features:
  • • While entering a number, the X register of the stack display reflects the main display
  • • No stack display in timer mode
  • • Added localized day of week names (English, German, French, Italian, Spanish, Portuguese)

1.4.5 – March 30, 2012
    New Features:
  • • LinEq (Linear Equation solver) now handles complex numbers

1.4.0 – March 16, 2012
  • • Name change of app for easy differentiation between iPad and iPhone versions
    • Improved input of dates: automatic swapping of day and month (if unambiguous), year optional for current year
    • Date shown correctly in SCI display mode. Year separated by additional decimal point.
    • Single- or double-tap on display to show register pop-up
    • Triple-tap on display to turn calculator off
    • New button to toggle stack display
    • "Store DP Setting as Default" behaviour is now more intuitive
    • CLEAR does not affect extended memory registers
    • The percent key works also in complex mode

    Bug Fix:
  • • Correct state when interrupting a pending hyperbolic function with STO or RCL

1.3.0 – February 12, 2012
    New Features:
  • Renamed and enhanced day-of-week function: day of week is shown as text. Entering an integer allows you to determine the day of the week and the date of any date a given number of days in the future or past.
  • Enabling the stack register display also shows the Last X register.
  • Various optimizations.

1.2.0 – June 17, 2011
    New Features:
  • Replaced financial functions (now available in free RPN-70 Calc app) by INT (integer part), FRAC (fractional part), and RAN# (random number).

1.1.1 – May 17, 2011
  • Bug Fixes:
  • Fixed embarrassing bug introduced with the previous version which prevented the display from going blank on power-off.

  • New Features:
  • Large display digits. For improved readability, large digits may be used in place of the LEDs of the original HP-45. Turn them on in the settings panel.

1.1.0 – May 11, 2011
  • Bugfixes:
  • Raising a negative value to the power of the inverse of an even integer returned a correct result in complex mode only.
  • Entering π when the display only contains a decimal point in some cases wouldn't push a zero on the stack.

  • New Features:
  • Hyperbolic functions (sinh, cosh, tanh) and their inverse functions, both for real and complex numbers. This is a user setting. When on, then angular mode decimal grads (GRD) is not available.
  • New user setting "Enable Stack Display" shows the stack directly on face of the calculator. Single-tap area above gold key to show or hide. In complex mode: double-tap to turn on, single-tap to alternate between real and imaginary parts of complex numbers.
  • Function "Conj" to get the conjugate of a complex number.
  • Relabeled key →P to →∠ (phasor form) in complex mode to better show its function (convert rectangular form to phasor form).
  • New background images.

1.0.3 – April 11, 2011
  • Bugfixes:
  • In complex mode, completing the input of a real value with a stack operation didn't clear the imaginary part of the value.
  • Certain combinations of extreme input values for the financial functions could crash the application.
  • In certain regions, a result overflow would crash the app. Fixed display problems for Arabic and Indian regions.

  • New Features:
  • All multi-key operations now have visual status indicators. Multi-key operations may be aborted anytime.
  • Keys 1 through 3 have labels while they serve for selecting a background.
  • The factorial function n! now handles complex numbers.
  • Register operations using the Σ+ key (which affect x, y and R7, R8 simultaneously) now have unrestricted functionality. They may involve extended registers, complex numbers and the entire set of register arithmetic operations. Useful for working with data pairs.
  • On switching to the complex mode, the stack is copied to the complex stack X and Y.

1.0.2 – March 28, 2011
  • Bugfixes:
  • Julian calender showed Gregorian weekdays between Oct 15 and Dec 31 of 1582.
  • Certain Julian calendar leap year dates, like Feb 29, 1700, were rejected.
  • The imaginary part of the complex arc sine in some cases had the wrong sign.
  • Fixed behavior of →D.MS function, which was different from HP-45 in some angular modes.

  • New Features:
  • Calculating with complex number has been redesigned to work like on the HP-15C.
  • After leaving the complex mode, the last used complex x and y values are available on the stack.
  • arc sin and arc cos may now be calculated for values outside of the range -1 to +1. The result is a complex value.
  • Factorial of a negative integer is now shown as "complex infinity".
  • A single-value format for entering dates has been added: d.mmyyyy. Julian calendar is used if the value is negative. Both old and new formats are detected automatically. For the regions U.S.A. and English-speaking Canada, the day/month order is reversed.

1.0.1 – March 17, 2011
  • First public version.

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