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 the iPhone.
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.

Features

• Complete. All functions and operations of the HP-45 have been implemented. You may even access the inofficial timer and use it as a clock or as a stopwatch with up to 9 lap times. Choose between the HP-45's original calculation speed and the blazingly fast speed of your device.


• Super-45. To have your HP-45 do really amazing things, turn on the "Super-45" mode. (Note that RPN-45 SD always works in Super-45 mode.) Perform all kinds of calculations on complex numbers, use twice as many memory registers (making them non-volatile at the same time), get additional functions, unlock the expanded capabilities of standard functions, and enjoy a number of user interface improvements. Or even let your HP-45 solve common equations, statistical and date problems.


• Made for iOS. View all stack and memory registers at a glance. Or the stopwatch's lap times. Exchange results with other applications using cut/copy/paste. Discard wrongly entered numbers with a quick swipe across the display.


• Versatile. Modify the calculator to your liking. Replace the rarely used GRD setting with HYP and get hyperbolic functions. Set the timer's capacity to either 12 or 100 hours. Replace HP's LED display by larger digits.


• Printer. Print your results on the built-in paper tape printer. Optionally show negative results in red. Log your key-presses on the paper tape. Delete lines or insert empty lines. Send the paper tape via e-mail or print it on any AirPrint-compatible printer. Select your favorite ribbon color.




On RPN-45 HD only:

• Built-in manual. A total of seven screens describing the functions and operations of the HP-45, the timer, and the extended functions of RPN-45 are available right in the application. A short introduction to calculating using RPN is included.


• More options. Use the timer as a chess clock. Choose from 30 different background pictures, or add your own. Turn the keyclick sound on or off. See a "live" view of the stack registers. Add arbitrary text to the printer tape.

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

• Neu:
• • New unit troy ounce
    Pressing the gold key, followed by the x-key, toggles between ounce (oz) and troy ounce (ozt).

• New:
• • Faster startup – no delay until the first button press is recognized after switching on.

• New:
• • (Vintage-45): If Extras are turned on
    - A number like 9.9e99 will show up as 1.e100 when the format SCI 0 is selected.
    - Calling up the stopwatch (RCL ENTER) initially shows a running clock in 12-hour format.
      Store up to 10 time values by pressing any key from 0 to 9.
  
  • (RPN-45 HD): Avoids a possible crash when the calculator is not set to Super-45 mode.
  

• New:
• • In "Super-45" mode, results such as 9.99×10⁹⁹ now appear correctly rounded both in the display and on the printer
    for all decimal point settings, e.g. SCI 1 (in contrast to the original HP-45).
• • Certain calculations, e.g. 100⁷⁵, caused the app to crash.

• New:
• • The low-battery indicator, i.e. all decimal points lit, is suppressed on Silicon Macs.

• New:
• • The low-battery indicator, i.e. all decimal points lit, is suppressed on Silicon Macs.
• • Visual adjustments to iPhone 16 Pro and Pro Max

• New:
• • Toggle LED display versus high-contrast display: "gold key" double-tap display.
• • Toggle thousand separators on/off: "gold key" triple-tap display.

• New:
• • Runs on Apple Silicon Macs (Notes)

• New:
• • (RPN-45 HD & SD): Key-flashing ("Flash Keys") may be turned on or off in Settings.
• • (RPN-45 SD): Improved detection of the type of cubic equation solutions.
• • (Vintage-45): Fixes possible rounding error in FIX mode. Runs on Apple Silicon Macs.

• New:
• • Control haptic feedback (iPhones only):
    – Store 1939010x in R0 to set the level to x (1..3, 0 for off).
    – Recall R0 to see the current level.
     (RPN-45 SD): Haptic feedback may also be configured in RPN-45 SD's settings.
   "Sounds & Haptics" / "System Haptics" must be ON in the iPhone's settings.

• (Vintage-45): Storing 19390101 in R1 toggles key-flashing on and off.
  – Recalling 19390100 from R1 turns key-flashing off.
  – Recalling 19390101 from R1 turns key-flashing on.

(Note: Hewlett-Packard Company was founded on January 1, 1939.)

• New:
• • Improved handling of thousands separators
• • (RPN-45 HD) Registers are now saved when turning the calculator off.
• • (RPN-45 SD) Thousands separators now also appear in the high-contrast display.

• Bug Fixes:
• • (RPN-45 HD) When using an external keyboard, some keys were unresponsive in iOS 15.
• • (RPN-45 SD) High-contrast display didn't always place the exponent at the far right.

• New:
• • Improved calendar calculations:
  – Date range is Jan 1, 0001 to Dec 31, 9999.
  – For any date, the day-of-the-week is shown fully spelled out.
  – Enter a date as mm.ddyyyy (US, Canada) or dd.mmyyyy (elsewhere), then execute DATE.
  – A positive input is interpreted as Gregorian, a negative input as Julian.
  – Convert any date from Gregorian to Julian (and vice versa) by executing DATE.
  – Enter an integer n, execute DATE to see the date n days later or earlier than the date in Y.
     If the date in Y is invalid, the last valid date is used. (The current date, if none is available.)
     Y shows the Julian Day Number of the displayed date.
  – If Y = 0:
       0 DATE returns the current date.
       n DATE returns the Easter date of the year n (n = 1583 to 4099).
       j DATE returns the date corresponding to the Julian Day Number j (Gregorian if j is positive, Julian otherwise; j = 1,721,424 to 5,373,484)
  – Execute ∆DYS to get the number of days from date Y to date X.
     Y shows the result based on the 30 days/month calendar.

• Bug Fixes:
• • (RPN-45 HD) Stack values didn't show correctly in the register view popup in portrait mode.
• • (Vintage-45. v2.3) Results are now rounded to 12 digits internally.

• New:
• • iPad mini (2021) compatibility

• New:
• • Suppressed clipboard notification on each keypress (on iOS 14)

• Bug Fix:
• • An empty clipboard could cause a crash on startup

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

• Bug Fix:
• • RND didn't work correctly in regions using comma as decimal point

New:
• • New function ABS (gold-gold-6). Especially useful with complex numbers.
• 
  (HD only):
• • New or changed commands for external keyboard:
    – ⇧ ⌘ S  thousand's separators on/off
    – >  swaps registers R0…R9 and R.0…R.9
    – ⌘ P  show/hide printer
    – ⌥ ⌫  CLR A (clear stack and all registers)
    – ⌥ L  LAST x (was ⌘-L)
    – ⌃ 1/2/3  set ribbon color to black/blue/green
    – ⇧⌃⌥S  backup registers
    – ⇧⌃⌥R  recall registers from backup
    – ⇧⌃⌥<  exchange registers with backup
  – ⇧⌃⌥N  reset calculator

  Download the complete list (version 1.1).

New:
• • Additional commands for external keyboard:
    – ⇧K: stack display on/off
    – ⌥P: π
    – ⌃$: ∑-

Bug Fix:
• • Ending timer mode using the ENTER key didn't restore the decimal key legend

New:
• • (HD) Additional commands for external keyboard:
    – ⇧F: selects purple key functions (same as pressing gold key twice)
    – N: executes n!
    – D: executes ∆% (percent difference)
• • (HD) Simplified installation of user background image via Files app (see "Background Image")
• • Key flashing may be turned off and on:
    – Store 19390101 in R1 to turn off
    – Recall 19390101 from R1 to turn on
      (Hewlett-Packard Company was founded on Jan 1, 1939)
• • In TRACE mode, the Easter date function is now clearly marked

Bug Fixes (HD):
• • The "Roll down" key didn't always show the correct arrow
• • Some keys used in timer modes didn't show their key-down image
• • The external keyboard command "s" (STO) was nonoperational

New:
• • Full support of hardware keyboard.
• • HYP mode may be cancelled by pressing the EEX key again.
• • Printer mode ALL is now called TRACE.
• • Portrait mode is back.

Bug Fixes:
• • Gold key + EEX was logged as GRD instead of HYP.
• • Logging chess moves would print out unneeded lines.
• • Move count of chess player 2 would not be updated in portrait mode register view.
• • Using scientific notation could crash the app in some regions, i.e. Australia, Sweden, Slovenia.

New:
• • HYP mode may be cancelled by pressing the EEX key again

Bug Fix:
• • Using scientific notation could crash the app in some regions, i.e. Australia, Sweden, Slovenia.

New:
• • Stack display: LastX may be shown or hidden independently from other stack registers. Simply tap on their respective areas.
• • Dark Mode compatibility
• • The rarely used portrait mode has been dropped.

Bug Fixes:
• • Overflow value now shows correctly in SCI/ENG display modes
• • Executing the summation command ∑ with a very large argument would cause a crash
• • Calling up and saving settings while entering a number with an exponent would cause a crash on the next digit input
• • The operation FIX 0 was logged on the printer as "FIX S" instead of "FIX 0"
• • Gold-7 and Gold-8 were not logged as REGS and STACK
• • Chess mode now shows RUN or STOP on printer (not CHS) after pressing R/S

New:
• • 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)

New:
• • 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

New:
• • 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)

New:
• • 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)

New:
• • 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

New:
• • Better FRAC results for large arguments

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

New:
• • 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

New:
• • 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

New:
• • 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

New:
• • 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

New:
• • 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

New:
• • 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

New:
• • 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

New:
• • In SCI and ENG notation, command RND now rounds the mantissa only, not the entire number

New:
• • 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]

New:
• • 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

New:
• • 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

New:
• • NEW FUNCTIONS:
  - 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

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)

New Features:
• • LinEq (Linear Equation solver) now handles complex numbers
  

New:
• • 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

First release of RPN-45 SD (V1.4.0)
First release of Vintage-45 (V1.0.3): March 7, 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.

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

• 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.

• 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.

• 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.

• 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.

• First public version.